diff --git a/Documentation/rest-api-changes.txt b/Documentation/rest-api-changes.txt
index 65275bd..2f144c6 100644
--- a/Documentation/rest-api-changes.txt
+++ b/Documentation/rest-api-changes.txt
@@ -7216,11 +7216,16 @@
 Whether the new change should be set to work in progress.
 |`base_change`        |optional|
 A link:#change-id[\{change-id\}] that identifies the base change for a create
-change operation. Mutually exclusive with `base_commit`.
+change operation. +
+Mutually exclusive with `base_commit`. +
+If neither `base_commit` nor `base_change` are set, the target branch tip will
+be used as the parent commit.
 |`base_commit`        |optional|
 A 40-digit hex SHA-1 of the commit which will be the parent commit of the newly
-created change. If set, it must be a merged commit on the destination branch.
-Mutually exclusive with `base_change`.
+created change. If set, it must be a merged commit on the destination branch. +
+Mutually exclusive with `base_change`. +
+If neither `base_commit` nor `base_change` are set, the target branch tip will
+be used as the parent commit.
 |`new_branch`         |optional, default to `false`|
 Allow creating a new branch when set to `true`. Using this option is
 only possible for non-merge commits (if the `merge` field is not set).
diff --git a/java/com/google/gerrit/server/account/GroupCache.java b/java/com/google/gerrit/server/account/GroupCache.java
index 1e28d7d..46c730c 100644
--- a/java/com/google/gerrit/server/account/GroupCache.java
+++ b/java/com/google/gerrit/server/account/GroupCache.java
@@ -14,11 +14,15 @@
 
 package com.google.gerrit.server.account;
 
+import com.google.gerrit.common.UsedAt;
+import com.google.gerrit.common.UsedAt.Project;
 import com.google.gerrit.entities.AccountGroup;
 import com.google.gerrit.entities.InternalGroup;
+import com.google.gerrit.exceptions.StorageException;
 import java.util.Collection;
 import java.util.Map;
 import java.util.Optional;
+import org.eclipse.jgit.lib.ObjectId;
 
 /** Tracks group objects in memory for efficient access. */
 public interface GroupCache {
@@ -62,6 +66,22 @@
   Map<AccountGroup.UUID, InternalGroup> get(Collection<AccountGroup.UUID> groupUuids);
 
   /**
+   * Returns an {@code InternalGroup} instance for the given {@code AccountGroup.UUID} at the given
+   * {@code metaId} of {@link com.google.gerrit.entities.RefNames#refsGroups} ref.
+   *
+   * <p>The caller is responsible to ensure the presence of {@code metaId} and the corresponding
+   * meta ref.
+   *
+   * @param groupUuid the UUID of the internal group
+   * @param metaId the sha1 of commit in {@link com.google.gerrit.entities.RefNames#refsGroups} ref.
+   * @return the internal group at specific sha1 {@code metaId}
+   * @throws StorageException if no internal group with this UUID exists on this server at the
+   *     specific sha1, or if an error occurred during lookup.
+   */
+  @UsedAt(Project.GOOGLE)
+  InternalGroup getFromMetaId(AccountGroup.UUID groupUuid, ObjectId metaId) throws StorageException;
+
+  /**
    * Removes the association of the given ID with a group.
    *
    * <p>The next call to {@link #get(AccountGroup.Id)} won't provide a cached value.
diff --git a/java/com/google/gerrit/server/account/GroupCacheImpl.java b/java/com/google/gerrit/server/account/GroupCacheImpl.java
index 2d947ba..6f4fce9 100644
--- a/java/com/google/gerrit/server/account/GroupCacheImpl.java
+++ b/java/com/google/gerrit/server/account/GroupCacheImpl.java
@@ -27,6 +27,7 @@
 import com.google.gerrit.entities.AccountGroup;
 import com.google.gerrit.entities.InternalGroup;
 import com.google.gerrit.entities.RefNames;
+import com.google.gerrit.exceptions.StorageException;
 import com.google.gerrit.proto.Protos;
 import com.google.gerrit.server.cache.CacheModule;
 import com.google.gerrit.server.cache.proto.Cache;
@@ -122,15 +123,19 @@
   private final LoadingCache<AccountGroup.Id, Optional<InternalGroup>> byId;
   private final LoadingCache<String, Optional<InternalGroup>> byName;
   private final LoadingCache<String, Optional<InternalGroup>> byUUID;
+  private final LoadingCache<Cache.GroupKeyProto, InternalGroup> persistedByUuidCache;
 
   @Inject
   GroupCacheImpl(
       @Named(BYID_NAME) LoadingCache<AccountGroup.Id, Optional<InternalGroup>> byId,
       @Named(BYNAME_NAME) LoadingCache<String, Optional<InternalGroup>> byName,
-      @Named(BYUUID_NAME) LoadingCache<String, Optional<InternalGroup>> byUUID) {
+      @Named(BYUUID_NAME) LoadingCache<String, Optional<InternalGroup>> byUUID,
+      @Named(BYUUID_NAME_PERSISTED)
+          LoadingCache<Cache.GroupKeyProto, InternalGroup> persistedByUuidCache) {
     this.byId = byId;
     this.byName = byName;
     this.byUUID = byUUID;
+    this.persistedByUuidCache = persistedByUuidCache;
   }
 
   @Override
@@ -185,6 +190,21 @@
   }
 
   @Override
+  public InternalGroup getFromMetaId(AccountGroup.UUID groupUuid, ObjectId metaId)
+      throws StorageException {
+    Cache.GroupKeyProto key =
+        Cache.GroupKeyProto.newBuilder()
+            .setUuid(groupUuid.get())
+            .setRevision(ObjectIdConverter.create().toByteString(metaId))
+            .build();
+    try {
+      return persistedByUuidCache.get(key);
+    } catch (ExecutionException e) {
+      throw new StorageException(e);
+    }
+  }
+
+  @Override
   public void evict(AccountGroup.Id groupId) {
     if (groupId != null) {
       logger.atFine().log("Evict group %s by ID", groupId.get());
diff --git a/java/com/google/gerrit/server/project/ProjectCacheImpl.java b/java/com/google/gerrit/server/project/ProjectCacheImpl.java
index 6498d1b..0afaa3f 100644
--- a/java/com/google/gerrit/server/project/ProjectCacheImpl.java
+++ b/java/com/google/gerrit/server/project/ProjectCacheImpl.java
@@ -76,6 +76,7 @@
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.locks.Lock;
 import java.util.concurrent.locks.ReentrantLock;
+import java.util.stream.Stream;
 import org.eclipse.jgit.errors.ConfigInvalidException;
 import org.eclipse.jgit.errors.RepositoryNotFoundException;
 import org.eclipse.jgit.lib.Config;
@@ -300,19 +301,20 @@
   @Override
   public Set<AccountGroup.UUID> guessRelevantGroupUUIDs() {
     try (Timer0.Context ignored = guessRelevantGroupsLatency.start()) {
+      Stream<AccountGroup.UUID> configuredRelevantGroups =
+          Arrays.stream(config.getStringList("groups", /* subsection= */ null, "relevantGroup"))
+              .map(AccountGroup::uuid);
+
+      Stream<AccountGroup.UUID> guessedRelevantGroups =
+          inMemoryProjectCache.asMap().values().stream()
+              .filter(Objects::nonNull)
+              .flatMap(p -> p.getAllGroupUUIDs().stream())
+              // getAllGroupUUIDs shouldn't really return null UUIDs, but harden
+              // against them just in case there is a bug or corner case.
+              .filter(id -> id != null && id.get() != null);
+
       Set<AccountGroup.UUID> relevantGroupUuids =
-          Streams.concat(
-                  Arrays.stream(
-                          config.getStringList("groups", /* subsection= */ null, "relevantGroup"))
-                      .map(AccountGroup::uuid),
-                  all().stream()
-                      .map(n -> inMemoryProjectCache.getIfPresent(n))
-                      .filter(Objects::nonNull)
-                      .flatMap(p -> p.getAllGroupUUIDs().stream())
-                      // getAllGroupUUIDs shouldn't really return null UUIDs, but harden
-                      // against them just in case there is a bug or corner case.
-                      .filter(id -> id != null && id.get() != null))
-              .collect(toSet());
+          Streams.concat(configuredRelevantGroups, guessedRelevantGroups).collect(toSet());
       logger.atFine().log("relevant group UUIDs: %s", relevantGroupUuids);
       return relevantGroupUuids;
     }
diff --git a/java/com/google/gerrit/server/query/account/AccountQueryBuilder.java b/java/com/google/gerrit/server/query/account/AccountQueryBuilder.java
index e31411c..d5c4a97 100644
--- a/java/com/google/gerrit/server/query/account/AccountQueryBuilder.java
+++ b/java/com/google/gerrit/server/query/account/AccountQueryBuilder.java
@@ -159,7 +159,7 @@
       return AccountPredicates.preferredEmail(email);
     }
 
-    throw new QueryParseException("'email' operator is not supported by account index version");
+    throw new QueryParseException("'email' operator is not supported on this gerrit host");
   }
 
   @Operator
diff --git a/java/com/google/gerrit/server/query/change/ChangeQueryBuilder.java b/java/com/google/gerrit/server/query/change/ChangeQueryBuilder.java
index 24d205d..da75057 100644
--- a/java/com/google/gerrit/server/query/change/ChangeQueryBuilder.java
+++ b/java/com/google/gerrit/server/query/change/ChangeQueryBuilder.java
@@ -694,7 +694,8 @@
 
     if ("mergeable".equalsIgnoreCase(value)) {
       if (!args.indexMergeable) {
-        throw new QueryParseException("'is:mergeable' operator is not supported by server");
+        throw new QueryParseException(
+            "'is:mergeable' operator is not supported on this gerrit host");
       }
       return new BooleanPredicate(ChangeField.MERGEABLE_SPEC);
     }
@@ -775,7 +776,7 @@
   @Operator
   public Predicate<ChangeData> conflicts(String value) throws QueryParseException {
     if (!args.conflictsPredicateEnabled) {
-      throw new QueryParseException("'conflicts:' operator is not supported by server");
+      throw new QueryParseException("'conflicts:' operator is not supported on this gerrit host");
     }
     List<Change> changes = parseChange(value);
     List<Predicate<ChangeData>> or = new ArrayList<>(changes.size());
@@ -1140,7 +1141,10 @@
   @Operator
   public Predicate<ChangeData> message(String text) throws QueryParseException {
     if (text.startsWith("^")) {
-      checkFieldAvailable(ChangeField.COMMIT_MESSAGE_EXACT, "messageexact");
+      if (!args.index.getSchema().hasField(ChangeField.COMMIT_MESSAGE_EXACT)) {
+        throw new QueryParseException(
+            "'message' operator with regular expression is not supported on this gerrit host");
+      }
       return new RegexMessagePredicate(text);
     }
     return ChangePredicates.message(text);
@@ -1645,7 +1649,7 @@
       throws QueryParseException {
     if (!args.index.getSchema().hasField(field)) {
       throw new QueryParseException(
-          String.format("'%s' operator is not supported by change index version", operator));
+          String.format("'%s' operator is not supported on this gerrit host", operator));
     }
   }
 
diff --git a/java/com/google/gerrit/server/restapi/change/PostReview.java b/java/com/google/gerrit/server/restapi/change/PostReview.java
index a8ba052..22eb32c 100644
--- a/java/com/google/gerrit/server/restapi/change/PostReview.java
+++ b/java/com/google/gerrit/server/restapi/change/PostReview.java
@@ -379,7 +379,8 @@
       // Add the review ops.
       logger.atFine().log("posting review");
       PostReviewOp postReviewOp =
-          postReviewOpFactory.create(projectState, revision.getPatchSet().id(), input);
+          postReviewOpFactory.create(
+              projectState, revision.getPatchSet().id(), input, revision.getAccountId());
       bu.addOp(revision.getChange().getId(), postReviewOp);
 
       // Adjust the attention set based on the input
diff --git a/java/com/google/gerrit/server/restapi/change/PostReviewOp.java b/java/com/google/gerrit/server/restapi/change/PostReviewOp.java
index b7d17f2..29e453b 100644
--- a/java/com/google/gerrit/server/restapi/change/PostReviewOp.java
+++ b/java/com/google/gerrit/server/restapi/change/PostReviewOp.java
@@ -97,7 +97,8 @@
 
 public class PostReviewOp implements BatchUpdateOp {
   interface Factory {
-    PostReviewOp create(ProjectState projectState, PatchSet.Id psId, ReviewInput in);
+    PostReviewOp create(
+        ProjectState projectState, PatchSet.Id psId, ReviewInput in, Account.Id reviewerId);
   }
 
   /**
@@ -192,6 +193,7 @@
   private final ProjectState projectState;
   private final PatchSet.Id psId;
   private final ReviewInput in;
+  private final Account.Id reviewerId;
   private final boolean publishPatchSetLevelComment;
 
   private IdentifiedUser user;
@@ -220,7 +222,8 @@
       PluginSetContext<OnPostReview> onPostReviews,
       @Assisted ProjectState projectState,
       @Assisted PatchSet.Id psId,
-      @Assisted ReviewInput in) {
+      @Assisted ReviewInput in,
+      @Assisted Account.Id reviewerId) {
     this.approvalCopier = approvalCopier;
     this.approvalsUtil = approvalsUtil;
     this.publishCommentUtil = publishCommentUtil;
@@ -237,6 +240,7 @@
     this.projectState = projectState;
     this.psId = psId;
     this.in = in;
+    this.reviewerId = reviewerId;
   }
 
   @Override
@@ -645,10 +649,11 @@
           del.add(c);
           update.putApproval(normName, (short) 0);
         }
-        // Only allow voting again if the vote is copied over from a past patch-set, or the
-        // values are different.
+        // Only allow voting again the values are different, if the real account differs or if the
+        // vote is copied over from a past patch-set.
       } else if (c != null
           && (c.value() != ent.getValue()
+              || !c.realAccountId().equals(reviewerId)
               || (inLabels.containsKey(c.label()) && isApprovalCopiedOver(c, ctx.getNotes())))) {
         PatchSetApproval.Builder b =
             c.toBuilder()
diff --git a/java/com/google/gerrit/server/restapi/project/CreateChange.java b/java/com/google/gerrit/server/restapi/project/CreateChange.java
index 59efd06..2f1153e 100644
--- a/java/com/google/gerrit/server/restapi/project/CreateChange.java
+++ b/java/com/google/gerrit/server/restapi/project/CreateChange.java
@@ -24,6 +24,7 @@
 import com.google.gerrit.extensions.restapi.RestApiException;
 import com.google.gerrit.extensions.restapi.RestModifyView;
 import com.google.gerrit.server.CurrentUser;
+import com.google.gerrit.server.ProjectUtil;
 import com.google.gerrit.server.permissions.PermissionBackendException;
 import com.google.gerrit.server.project.InvalidChangeOperationException;
 import com.google.gerrit.server.project.ProjectResource;
@@ -59,7 +60,8 @@
       throw new AuthException("Authentication required");
     }
 
-    if (!Strings.isNullOrEmpty(input.project) && !rsrc.getName().equals(input.project)) {
+    if (!Strings.isNullOrEmpty(input.project)
+        && !rsrc.getName().equals(ProjectUtil.sanitizeProjectName(input.project))) {
       throw new BadRequestException("project must match URL");
     }
 
diff --git a/javatests/com/google/gerrit/acceptance/api/group/GroupsIT.java b/javatests/com/google/gerrit/acceptance/api/group/GroupsIT.java
index d630296..04bdf15 100644
--- a/javatests/com/google/gerrit/acceptance/api/group/GroupsIT.java
+++ b/javatests/com/google/gerrit/acceptance/api/group/GroupsIT.java
@@ -601,6 +601,20 @@
   }
 
   @Test
+  public void getGroupFromMetaId() throws Exception {
+    AccountGroup.UUID uuid = groupOperations.newGroup().create();
+    InternalGroup preUpdateState = groupCache.get(uuid).get();
+    gApi.groups().id(uuid.toString()).description("New description");
+
+    InternalGroup postUpdateState = groupCache.get(uuid).get();
+    assertThat(postUpdateState).isNotEqualTo(preUpdateState);
+    assertThat(groupCache.getFromMetaId(uuid, preUpdateState.getRefState()))
+        .isEqualTo(preUpdateState);
+    assertThat(groupCache.getFromMetaId(uuid, postUpdateState.getRefState()))
+        .isEqualTo(postUpdateState);
+  }
+
+  @Test
   @GerritConfig(name = "groups.global:Anonymous-Users.name", value = "All Users")
   public void getSystemGroupByConfiguredName() throws Exception {
     GroupReference anonymousUsersGroup = systemGroupBackend.getGroup(ANONYMOUS_USERS);
diff --git a/javatests/com/google/gerrit/acceptance/rest/account/ImpersonationIT.java b/javatests/com/google/gerrit/acceptance/rest/account/ImpersonationIT.java
index eb827c0..3531d1c 100644
--- a/javatests/com/google/gerrit/acceptance/rest/account/ImpersonationIT.java
+++ b/javatests/com/google/gerrit/acceptance/rest/account/ImpersonationIT.java
@@ -20,6 +20,8 @@
 import static com.google.gerrit.acceptance.testsuite.project.TestProjectUpdate.allowLabel;
 import static com.google.gerrit.acceptance.testsuite.project.TestProjectUpdate.block;
 import static com.google.gerrit.acceptance.testsuite.project.TestProjectUpdate.capabilityKey;
+import static com.google.gerrit.entities.RefNames.changeMetaRef;
+import static com.google.gerrit.entities.RefNames.patchSetRef;
 import static com.google.gerrit.extensions.client.ListChangesOption.MESSAGES;
 import static com.google.gerrit.server.group.SystemGroupBackend.ANONYMOUS_USERS;
 import static com.google.gerrit.server.group.SystemGroupBackend.REGISTERED_USERS;
@@ -28,11 +30,13 @@
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.Iterables;
+import com.google.errorprone.annotations.CanIgnoreReturnValue;
 import com.google.gerrit.acceptance.AbstractDaemonTest;
 import com.google.gerrit.acceptance.PushOneCommit;
 import com.google.gerrit.acceptance.RestResponse;
 import com.google.gerrit.acceptance.RestSession;
 import com.google.gerrit.acceptance.TestAccount;
+import com.google.gerrit.acceptance.UseLocalDisk;
 import com.google.gerrit.acceptance.config.GerritConfig;
 import com.google.gerrit.acceptance.testsuite.project.ProjectOperations;
 import com.google.gerrit.acceptance.testsuite.request.RequestScopeOperations;
@@ -43,8 +47,10 @@
 import com.google.gerrit.entities.LabelId;
 import com.google.gerrit.entities.LabelType;
 import com.google.gerrit.entities.Patch;
+import com.google.gerrit.entities.PatchSet;
 import com.google.gerrit.entities.PatchSetApproval;
 import com.google.gerrit.entities.Permission;
+import com.google.gerrit.entities.Project;
 import com.google.gerrit.entities.RobotComment;
 import com.google.gerrit.extensions.api.changes.DraftInput;
 import com.google.gerrit.extensions.api.changes.ReviewInput;
@@ -55,6 +61,7 @@
 import com.google.gerrit.extensions.api.changes.SubmitInput;
 import com.google.gerrit.extensions.api.groups.GroupInput;
 import com.google.gerrit.extensions.client.Side;
+import com.google.gerrit.extensions.client.SubmitType;
 import com.google.gerrit.extensions.common.AccountInfo;
 import com.google.gerrit.extensions.common.ChangeInfo;
 import com.google.gerrit.extensions.common.ChangeMessageInfo;
@@ -71,8 +78,15 @@
 import com.google.gerrit.server.project.testing.TestLabels;
 import com.google.gerrit.server.query.change.ChangeData;
 import com.google.inject.Inject;
+import java.io.File;
+import java.io.IOException;
 import org.apache.http.Header;
 import org.apache.http.message.BasicHeader;
+import org.eclipse.jgit.internal.storage.dfs.InMemoryRepository;
+import org.eclipse.jgit.junit.TestRepository;
+import org.eclipse.jgit.lib.ReflogEntry;
+import org.eclipse.jgit.lib.Repository;
+import org.eclipse.jgit.revwalk.RevCommit;
 import org.junit.After;
 import org.junit.Before;
 import org.junit.Test;
@@ -105,28 +119,246 @@
   }
 
   @Test
+  @UseLocalDisk
   public void voteOnBehalfOf() throws Exception {
     allowCodeReviewOnBehalfOf();
+    TestAccount realUser = admin;
+    TestAccount impersonatedUser = user;
     PushOneCommit.Result r = createChange();
     RevisionApi revision = gApi.changes().id(r.getChangeId()).current();
 
+    try (Repository repo = repoManager.openRepository(project)) {
+      String changeMetaRef = changeMetaRef(r.getChange().getId());
+      createRefLogFileIfMissing(repo, changeMetaRef);
+
+      ReviewInput in = ReviewInput.recommend();
+      in.onBehalfOf = impersonatedUser.id().toString();
+      in.message = "Message on behalf of";
+      revision.review(in);
+
+      PatchSetApproval psa = Iterables.getOnlyElement(r.getChange().approvals().values());
+      assertThat(psa.patchSetId().get()).isEqualTo(1);
+      assertThat(psa.label()).isEqualTo("Code-Review");
+      assertThat(psa.accountId()).isEqualTo(impersonatedUser.id());
+      assertThat(psa.value()).isEqualTo(1);
+      assertThat(psa.realAccountId()).isEqualTo(realUser.id());
+
+      ChangeData cd = r.getChange();
+      ChangeMessage m = Iterables.getLast(cmUtil.byChange(cd.notes()));
+      assertThat(m.getMessage()).endsWith(in.message);
+      assertThat(m.getAuthor()).isEqualTo(impersonatedUser.id());
+      assertThat(m.getRealAuthor()).isEqualTo(realUser.id());
+
+      // The change meta commit is created by the server and has the impersonated user as the
+      // author.
+      // Person idents of users in NoteDb commits are obfuscated due to privacy reasons.
+      RevCommit changeMetaCommit = projectOperations.project(project).getHead(changeMetaRef);
+      assertThat(changeMetaCommit.getCommitterIdent().getEmailAddress())
+          .isEqualTo(serverIdent.get().getEmailAddress());
+      assertThat(changeMetaCommit.getAuthorIdent().getEmailAddress())
+          .isEqualTo(changeNoteUtil.getAccountIdAsEmailAddress(impersonatedUser.id()));
+
+      // The ref log for the change meta ref records the impersonated user.
+      ReflogEntry changeMetaRefLogEntry = repo.getReflogReader(changeMetaRef).getLastEntry();
+      assertThat(changeMetaRefLogEntry.getWho().getEmailAddress())
+          .isEqualTo(impersonatedUser.email());
+    }
+  }
+
+  @Test
+  public void overrideImpersonatedVoteWithOtherImpersonatedVote_sameValue() throws Exception {
+    allowCodeReviewOnBehalfOf();
+    TestAccount realUser = admin;
+    TestAccount realUser2 = admin2;
+    TestAccount impersonatedUser = user;
+    PushOneCommit.Result r = createChange();
+    RevisionApi revision = gApi.changes().id(r.getChangeId()).current();
+
+    // realUser votes Code-Review+1 on behalf of impersonatedUser
     ReviewInput in = ReviewInput.recommend();
-    in.onBehalfOf = user.id().toString();
+    in.onBehalfOf = impersonatedUser.id().toString();
     in.message = "Message on behalf of";
     revision.review(in);
 
     PatchSetApproval psa = Iterables.getOnlyElement(r.getChange().approvals().values());
     assertThat(psa.patchSetId().get()).isEqualTo(1);
     assertThat(psa.label()).isEqualTo("Code-Review");
-    assertThat(psa.accountId()).isEqualTo(user.id());
+    assertThat(psa.accountId()).isEqualTo(impersonatedUser.id());
     assertThat(psa.value()).isEqualTo(1);
-    assertThat(psa.realAccountId()).isEqualTo(admin.id());
+    assertThat(psa.realAccountId()).isEqualTo(realUser.id());
 
     ChangeData cd = r.getChange();
     ChangeMessage m = Iterables.getLast(cmUtil.byChange(cd.notes()));
     assertThat(m.getMessage()).endsWith(in.message);
-    assertThat(m.getAuthor()).isEqualTo(user.id());
-    assertThat(m.getRealAuthor()).isEqualTo(admin.id());
+    assertThat(m.getAuthor()).isEqualTo(impersonatedUser.id());
+    assertThat(m.getRealAuthor()).isEqualTo(realUser.id());
+
+    // realUser2 votes Code-Review+1 on behalf of impersonatedUser, this should override the
+    // impersonated Code-Review+1 of realUser with an impersonated Code-Review+1 of realUser2
+    requestScopeOperations.setApiUser(realUser2.id());
+    in = ReviewInput.recommend();
+    in.onBehalfOf = impersonatedUser.id().toString();
+    in.message = "Another message on behalf of";
+    gApi.changes().id(r.getChangeId()).current().review(in);
+
+    psa = Iterables.getOnlyElement(r.getChange().approvals().values());
+    assertThat(psa.patchSetId().get()).isEqualTo(1);
+    assertThat(psa.label()).isEqualTo("Code-Review");
+    assertThat(psa.accountId()).isEqualTo(impersonatedUser.id());
+    assertThat(psa.value()).isEqualTo(1);
+    assertThat(psa.realAccountId()).isEqualTo(realUser2.id());
+
+    cd = r.getChange();
+    m = Iterables.getLast(cmUtil.byChange(cd.notes()));
+    assertThat(m.getMessage()).endsWith(in.message);
+    assertThat(m.getAuthor()).isEqualTo(impersonatedUser.id());
+    assertThat(m.getRealAuthor()).isEqualTo(realUser2.id());
+  }
+
+  @Test
+  public void overrideImpersonatedVoteWithOtherImpersonatedVote_differentValue() throws Exception {
+    allowCodeReviewOnBehalfOf();
+    TestAccount realUser = admin;
+    TestAccount realUser2 = admin2;
+    TestAccount impersonatedUser = user;
+    PushOneCommit.Result r = createChange();
+    RevisionApi revision = gApi.changes().id(r.getChangeId()).current();
+
+    // realUser votes Code-Review+1 on behalf of impersonatedUser
+    ReviewInput in = ReviewInput.recommend();
+    in.onBehalfOf = impersonatedUser.id().toString();
+    in.message = "Message on behalf of";
+    revision.review(in);
+
+    PatchSetApproval psa = Iterables.getOnlyElement(r.getChange().approvals().values());
+    assertThat(psa.patchSetId().get()).isEqualTo(1);
+    assertThat(psa.label()).isEqualTo("Code-Review");
+    assertThat(psa.accountId()).isEqualTo(impersonatedUser.id());
+    assertThat(psa.value()).isEqualTo(1);
+    assertThat(psa.realAccountId()).isEqualTo(realUser.id());
+
+    ChangeData cd = r.getChange();
+    ChangeMessage m = Iterables.getLast(cmUtil.byChange(cd.notes()));
+    assertThat(m.getMessage()).endsWith(in.message);
+    assertThat(m.getAuthor()).isEqualTo(impersonatedUser.id());
+    assertThat(m.getRealAuthor()).isEqualTo(realUser.id());
+
+    // realUser2 votes Code-Review-1 on behalf of impersonatedUser, this should override the
+    // impersonated Code-Review+1 of realUser with an impersonated Code-Review-1 of realUser2
+    requestScopeOperations.setApiUser(realUser2.id());
+    in = ReviewInput.dislike();
+    in.onBehalfOf = impersonatedUser.id().toString();
+    in.message = "Another message on behalf of";
+    gApi.changes().id(r.getChangeId()).current().review(in);
+
+    psa = Iterables.getOnlyElement(r.getChange().approvals().values());
+    assertThat(psa.patchSetId().get()).isEqualTo(1);
+    assertThat(psa.label()).isEqualTo("Code-Review");
+    assertThat(psa.accountId()).isEqualTo(impersonatedUser.id());
+    assertThat(psa.value()).isEqualTo(-1);
+    assertThat(psa.realAccountId()).isEqualTo(realUser2.id());
+
+    cd = r.getChange();
+    m = Iterables.getLast(cmUtil.byChange(cd.notes()));
+    assertThat(m.getMessage()).endsWith(in.message);
+    assertThat(m.getAuthor()).isEqualTo(impersonatedUser.id());
+    assertThat(m.getRealAuthor()).isEqualTo(realUser2.id());
+  }
+
+  @Test
+  public void overrideImpersonatedVoteWithNonImpersonatedVote_sameValue() throws Exception {
+    allowCodeReviewOnBehalfOf();
+    TestAccount realUser = admin;
+    TestAccount impersonatedUser = user;
+    PushOneCommit.Result r = createChange();
+    RevisionApi revision = gApi.changes().id(r.getChangeId()).current();
+
+    // realUser votes Code-Review+1 on behalf of impersonatedUser
+    ReviewInput in = ReviewInput.recommend();
+    in.onBehalfOf = impersonatedUser.id().toString();
+    in.message = "Message on behalf of";
+    revision.review(in);
+
+    PatchSetApproval psa = Iterables.getOnlyElement(r.getChange().approvals().values());
+    assertThat(psa.patchSetId().get()).isEqualTo(1);
+    assertThat(psa.label()).isEqualTo("Code-Review");
+    assertThat(psa.accountId()).isEqualTo(impersonatedUser.id());
+    assertThat(psa.value()).isEqualTo(1);
+    assertThat(psa.realAccountId()).isEqualTo(realUser.id());
+
+    ChangeData cd = r.getChange();
+    ChangeMessage m = Iterables.getLast(cmUtil.byChange(cd.notes()));
+    assertThat(m.getMessage()).endsWith(in.message);
+    assertThat(m.getAuthor()).isEqualTo(impersonatedUser.id());
+    assertThat(m.getRealAuthor()).isEqualTo(realUser.id());
+
+    // impersonatedUser votes Code-Review+1 themselves, this should override the impersonated
+    // Code-Review+1 with a non-impersonated Code-Review+1
+    requestScopeOperations.setApiUser(impersonatedUser.id());
+    in = ReviewInput.recommend();
+    in.message = "Message";
+    gApi.changes().id(r.getChangeId()).current().review(in);
+
+    psa = Iterables.getOnlyElement(r.getChange().approvals().values());
+    assertThat(psa.patchSetId().get()).isEqualTo(1);
+    assertThat(psa.label()).isEqualTo("Code-Review");
+    assertThat(psa.accountId()).isEqualTo(impersonatedUser.id());
+    assertThat(psa.value()).isEqualTo(1);
+    assertThat(psa.realAccountId()).isEqualTo(impersonatedUser.id());
+
+    cd = r.getChange();
+    m = Iterables.getLast(cmUtil.byChange(cd.notes()));
+    assertThat(m.getMessage()).endsWith(in.message);
+    assertThat(m.getAuthor()).isEqualTo(impersonatedUser.id());
+    assertThat(m.getRealAuthor()).isEqualTo(impersonatedUser.id());
+  }
+
+  @Test
+  public void overrideImpersonatedVoteWithNonImpersonatedVote_differentValue() throws Exception {
+    allowCodeReviewOnBehalfOf();
+    TestAccount realUser = admin;
+    TestAccount impersonatedUser = user;
+    PushOneCommit.Result r = createChange();
+    RevisionApi revision = gApi.changes().id(r.getChangeId()).current();
+
+    // realUser votes Code-Review+1 on behalf of impersonatedUser
+    ReviewInput in = ReviewInput.recommend();
+    in.onBehalfOf = impersonatedUser.id().toString();
+    in.message = "Message on behalf of";
+    revision.review(in);
+
+    PatchSetApproval psa = Iterables.getOnlyElement(r.getChange().approvals().values());
+    assertThat(psa.patchSetId().get()).isEqualTo(1);
+    assertThat(psa.label()).isEqualTo("Code-Review");
+    assertThat(psa.accountId()).isEqualTo(impersonatedUser.id());
+    assertThat(psa.value()).isEqualTo(1);
+    assertThat(psa.realAccountId()).isEqualTo(realUser.id());
+
+    ChangeData cd = r.getChange();
+    ChangeMessage m = Iterables.getLast(cmUtil.byChange(cd.notes()));
+    assertThat(m.getMessage()).endsWith(in.message);
+    assertThat(m.getAuthor()).isEqualTo(impersonatedUser.id());
+    assertThat(m.getRealAuthor()).isEqualTo(realUser.id());
+
+    // impersonatedUser votes Code-Review-1 themselves, this should override the impersonated
+    // Code-Review+1 with a non-impersonated Code-Review-1
+    requestScopeOperations.setApiUser(impersonatedUser.id());
+    in = ReviewInput.dislike();
+    in.message = "Message";
+    gApi.changes().id(r.getChangeId()).current().review(in);
+
+    psa = Iterables.getOnlyElement(r.getChange().approvals().values());
+    assertThat(psa.patchSetId().get()).isEqualTo(1);
+    assertThat(psa.label()).isEqualTo("Code-Review");
+    assertThat(psa.accountId()).isEqualTo(impersonatedUser.id());
+    assertThat(psa.value()).isEqualTo(-1);
+    assertThat(psa.realAccountId()).isEqualTo(impersonatedUser.id());
+
+    cd = r.getChange();
+    m = Iterables.getLast(cmUtil.byChange(cd.notes()));
+    assertThat(m.getMessage()).endsWith(in.message);
+    assertThat(m.getAuthor()).isEqualTo(impersonatedUser.id());
+    assertThat(m.getRealAuthor()).isEqualTo(impersonatedUser.id());
   }
 
   @Test
@@ -342,21 +574,120 @@
   }
 
   @Test
-  public void submitOnBehalfOf() throws Exception {
-    allowSubmitOnBehalfOf();
-    PushOneCommit.Result r = createChange();
+  @UseLocalDisk
+  public void submitOnBehalfOf_mergeAlways() throws Exception {
+    TestAccount realUser = admin;
+    TestAccount impersonatedUser = admin2;
+
+    // Create a project with MERGE_ALWAYS submit strategy so that a merge commit is created on
+    // submit and we can verify its committer and author and the ref log for the update of the
+    // target branch.
+    Project.NameKey project =
+        projectOperations.newProject().submitType(SubmitType.MERGE_ALWAYS).create();
+
+    testSubmitOnBehalfOf(project, realUser, impersonatedUser);
+
+    // The merge commit is created by the server and has the impersonated user as the author.
+    RevCommit mergeCommit = projectOperations.project(project).getHead("refs/heads/master");
+    assertThat(mergeCommit.getCommitterIdent().getEmailAddress())
+        .isEqualTo(serverIdent.get().getEmailAddress());
+    assertThat(mergeCommit.getAuthorIdent().getEmailAddress()).isEqualTo(impersonatedUser.email());
+
+    // The ref log for the target branch records the impersonated user.
+    try (Repository repo = repoManager.openRepository(project)) {
+      ReflogEntry targetBranchRefLogEntry =
+          repo.getReflogReader("refs/heads/master").getLastEntry();
+      assertThat(targetBranchRefLogEntry.getWho().getEmailAddress())
+          .isEqualTo(impersonatedUser.email());
+    }
+  }
+
+  @Test
+  @UseLocalDisk
+  public void submitOnBehalfOf_rebaseAlways() throws Exception {
+    TestAccount realUser = admin;
+    TestAccount impersonatedUser = admin2;
+
+    // Create a project with REBASE_ALWAYS submit strategy so that a new patch set is created on
+    // submit and we can verify its committer and author and the ref log for the update of the
+    // patch set ref and the target branch.
+    Project.NameKey project =
+        projectOperations.newProject().submitType(SubmitType.REBASE_ALWAYS).create();
+
+    ChangeData cd = testSubmitOnBehalfOf(project, realUser, impersonatedUser);
+
+    // Rebase on submit is expected to create a new patch set.
+    assertThat(cd.currentPatchSet().id().get()).isEqualTo(2);
+
+    // The patch set commit is created by the impersonated user and has the real user as the author.
+    // Recording the real user as the author seems to a bug, we would expect the author to be the
+    // impersonated user.
+    RevCommit newPatchSetCommit =
+        projectOperations.project(project).getHead(cd.currentPatchSet().refName());
+    assertThat(newPatchSetCommit.getCommitterIdent().getEmailAddress())
+        .isEqualTo(impersonatedUser.email());
+    assertThat(newPatchSetCommit.getAuthorIdent().getEmailAddress()).isEqualTo(realUser.email());
+
+    try (Repository repo = repoManager.openRepository(project)) {
+      // The ref log for the patch set ref records the impersonated user.
+      ReflogEntry patchSetRefLogEntry =
+          repo.getReflogReader(cd.currentPatchSet().refName()).getLastEntry();
+      assertThat(patchSetRefLogEntry.getWho().getEmailAddress())
+          .isEqualTo(impersonatedUser.email());
+
+      // The ref log for the target branch records the impersonated user.
+      ReflogEntry targetBranchRefLogEntry =
+          repo.getReflogReader("refs/heads/master").getLastEntry();
+      assertThat(targetBranchRefLogEntry.getWho().getEmailAddress())
+          .isEqualTo(impersonatedUser.email());
+    }
+  }
+
+  @CanIgnoreReturnValue
+  private ChangeData testSubmitOnBehalfOf(
+      Project.NameKey project, TestAccount realUser, TestAccount impersonatedUser)
+      throws Exception {
+    allowSubmitOnBehalfOf(project);
+
+    TestRepository<InMemoryRepository> testRepo = cloneProject(project, realUser);
+
+    PushOneCommit.Result r = createChange(testRepo);
     String changeId = project.get() + "~master~" + r.getChangeId();
     gApi.changes().id(changeId).current().review(ReviewInput.approve());
     SubmitInput in = new SubmitInput();
-    in.onBehalfOf = admin2.email();
-    gApi.changes().id(changeId).current().submit(in);
+    in.onBehalfOf = impersonatedUser.email();
 
-    ChangeData cd = r.getChange();
-    assertThat(cd.change().isMerged()).isTrue();
-    PatchSetApproval submitter =
-        approvalsUtil.getSubmitter(cd.notes(), cd.change().currentPatchSetId());
-    assertThat(submitter.accountId()).isEqualTo(admin2.id());
-    assertThat(submitter.realAccountId()).isEqualTo(admin.id());
+    try (Repository repo = repoManager.openRepository(project)) {
+      String changeMetaRef = changeMetaRef(r.getChange().getId());
+      createRefLogFileIfMissing(repo, changeMetaRef);
+      createRefLogFileIfMissing(repo, "refs/heads/master");
+      createRefLogFileIfMissing(repo, patchSetRef(PatchSet.id(r.getChange().getId(), 2)));
+
+      gApi.changes().id(changeId).current().submit(in);
+
+      ChangeData cd = r.getChange();
+      assertThat(cd.change().isMerged()).isTrue();
+      PatchSetApproval submitter =
+          approvalsUtil.getSubmitter(cd.notes(), cd.change().currentPatchSetId());
+      assertThat(submitter.accountId()).isEqualTo(impersonatedUser.id());
+      assertThat(submitter.realAccountId()).isEqualTo(realUser.id());
+
+      // The change meta commit is created by the server and has the impersonated user as the
+      // author.
+      // Person idents of users in NoteDb commits are obfuscated due to privacy reasons.
+      RevCommit changeMetaCommit = projectOperations.project(project).getHead(changeMetaRef);
+      assertThat(changeMetaCommit.getCommitterIdent().getEmailAddress())
+          .isEqualTo(serverIdent.get().getEmailAddress());
+      assertThat(changeMetaCommit.getAuthorIdent().getEmailAddress())
+          .isEqualTo(changeNoteUtil.getAccountIdAsEmailAddress(impersonatedUser.id()));
+
+      // The ref log for the change meta ref records the impersonated user.
+      ReflogEntry changeMetaRefLogEntry = repo.getReflogReader(changeMetaRef).getLastEntry();
+      assertThat(changeMetaRefLogEntry.getWho().getEmailAddress())
+          .isEqualTo(impersonatedUser.email());
+
+      return cd;
+    }
   }
 
   @Test
@@ -591,6 +922,10 @@
   }
 
   private void allowSubmitOnBehalfOf() throws Exception {
+    allowSubmitOnBehalfOf(project);
+  }
+
+  private void allowSubmitOnBehalfOf(Project.NameKey project) throws Exception {
     String heads = "refs/heads/*";
     projectOperations
         .project(project)
@@ -630,4 +965,12 @@
   private static Header runAsHeader(Object user) {
     return new BasicHeader("X-Gerrit-RunAs", user.toString());
   }
+
+  private void createRefLogFileIfMissing(Repository repo, String ref) throws IOException {
+    File log = new File(repo.getDirectory(), "logs/" + ref);
+    if (!log.exists()) {
+      log.getParentFile().mkdirs();
+      assertThat(log.createNewFile()).isTrue();
+    }
+  }
 }
diff --git a/javatests/com/google/gerrit/acceptance/rest/project/CreateChangeIT.java b/javatests/com/google/gerrit/acceptance/rest/project/CreateChangeIT.java
index 0c221aa..7b42d93 100644
--- a/javatests/com/google/gerrit/acceptance/rest/project/CreateChangeIT.java
+++ b/javatests/com/google/gerrit/acceptance/rest/project/CreateChangeIT.java
@@ -14,6 +14,7 @@
 
 package com.google.gerrit.acceptance.rest.project;
 
+import static com.google.common.truth.Truth.assertThat;
 import static com.google.common.truth.Truth8.assertThat;
 import static com.google.gerrit.entities.RefNames.REFS_HEADS;
 
@@ -21,6 +22,7 @@
 import com.google.gerrit.acceptance.RestResponse;
 import com.google.gerrit.extensions.api.projects.BranchInput;
 import com.google.gerrit.extensions.common.ChangeInput;
+import com.google.gerrit.extensions.restapi.IdString;
 import org.junit.Test;
 
 public class CreateChangeIT extends AbstractDaemonTest {
@@ -43,7 +45,44 @@
     ChangeInput input = new ChangeInput();
     input.branch = "foo";
     input.subject = "subject";
-    RestResponse cr = adminRestSession.post("/projects/" + project.get() + "/create.change", input);
-    cr.assertCreated();
+    RestResponse response =
+        adminRestSession.post("/projects/" + project.get() + "/create.change", input);
+    response.assertCreated();
+  }
+
+  @Test
+  public void nonMatchingProjectIsRejected() throws Exception {
+    ChangeInput input = new ChangeInput();
+    input.project = "non-matching-project";
+    input.branch = "master";
+    input.subject = "subject";
+    RestResponse response =
+        adminRestSession.post("/projects/" + project.get() + "/create.change", input);
+    response.assertBadRequest();
+    assertThat(response.getEntityContent()).isEqualTo("project must match URL");
+  }
+
+  @Test
+  public void matchingProjectIsAccepted() throws Exception {
+    ChangeInput input = new ChangeInput();
+    input.project = project.get();
+    input.branch = "master";
+    input.subject = "subject";
+    RestResponse response =
+        adminRestSession.post("/projects/" + project.get() + "/create.change", input);
+    response.assertCreated();
+  }
+
+  @Test
+  public void matchingProjectWithTrailingSlashIsAccepted() throws Exception {
+    ChangeInput input = new ChangeInput();
+    input.project = project.get() + "/";
+    input.branch = "master";
+    input.subject = "subject";
+    RestResponse response =
+        adminRestSession.post(
+            "/projects/" + IdString.fromDecoded(project.get() + "/").encoded() + "/create.change",
+            input);
+    response.assertCreated();
   }
 }
diff --git a/javatests/com/google/gerrit/server/query/change/AbstractQueryChangesTest.java b/javatests/com/google/gerrit/server/query/change/AbstractQueryChangesTest.java
index 5d38c55..fbf9c87 100644
--- a/javatests/com/google/gerrit/server/query/change/AbstractQueryChangesTest.java
+++ b/javatests/com/google/gerrit/server/query/change/AbstractQueryChangesTest.java
@@ -4064,7 +4064,7 @@
     assertThat(thrown.getCause()).isInstanceOf(QueryParseException.class);
     assertThat(thrown)
         .hasMessageThat()
-        .contains("'is:mergeable' operator is not supported by server");
+        .contains("'is:mergeable' operator is not supported on this gerrit host");
   }
 
   protected ChangeInserter newChangeForCommit(TestRepository<Repository> repo, RevCommit commit)
diff --git a/javatests/com/google/gerrit/server/query/group/AbstractQueryGroupsTest.java b/javatests/com/google/gerrit/server/query/group/AbstractQueryGroupsTest.java
index 540416f..b263ab6 100644
--- a/javatests/com/google/gerrit/server/query/group/AbstractQueryGroupsTest.java
+++ b/javatests/com/google/gerrit/server/query/group/AbstractQueryGroupsTest.java
@@ -401,9 +401,8 @@
     String query = "uuid:" + uuid;
     assertQuery(query, group);
 
-    for (GroupIndex index : groupIndexes.getWriteIndexes()) {
-      index.delete(uuid);
-    }
+    deleteGroup(uuid);
+
     assertQuery(query);
   }
 
@@ -441,6 +440,12 @@
     return createGroupWithDescription(name, null, members);
   }
 
+  protected void deleteGroup(AccountGroup.UUID uuid) throws Exception {
+    for (GroupIndex index : groupIndexes.getWriteIndexes()) {
+      index.delete(uuid);
+    }
+  }
+
   protected GroupInfo createGroupWithDescription(
       String name, String description, AccountInfo... members) throws Exception {
     GroupInput in = new GroupInput();
diff --git a/polygerrit-ui/app/elements/admin/gr-create-change-dialog/gr-create-file-edit-dialog.ts b/polygerrit-ui/app/elements/admin/gr-create-change-dialog/gr-create-file-edit-dialog.ts
index c3f79c7..0cfbaa4 100644
--- a/polygerrit-ui/app/elements/admin/gr-create-change-dialog/gr-create-file-edit-dialog.ts
+++ b/polygerrit-ui/app/elements/admin/gr-create-change-dialog/gr-create-file-edit-dialog.ts
@@ -14,7 +14,7 @@
 import {LitElement, html, nothing} from 'lit';
 import {customElement, property, query, state} from 'lit/decorators.js';
 import {resolve} from '../../../models/dependency';
-import {createEditUrl} from '../../../models/views/edit';
+import {createEditUrl} from '../../../models/views/change';
 import {modalStyles} from '../../../styles/gr-modal-styles';
 import {assertIsDefined} from '../../../utils/common-util';
 import {when} from 'lit/directives/when.js';
@@ -162,8 +162,8 @@
     const url = createEditUrl({
       changeNum: change._number,
       repo: change.project,
-      path: this.path,
       patchNum: 1 as PatchSetNumber,
+      editView: {path: this.path},
     });
     this.getNavigation().setUrl(url);
   }
diff --git a/polygerrit-ui/app/elements/admin/gr-repo-commands/gr-repo-commands.ts b/polygerrit-ui/app/elements/admin/gr-repo-commands/gr-repo-commands.ts
index 115bc43..11cfaab 100644
--- a/polygerrit-ui/app/elements/admin/gr-repo-commands/gr-repo-commands.ts
+++ b/polygerrit-ui/app/elements/admin/gr-repo-commands/gr-repo-commands.ts
@@ -31,7 +31,7 @@
 import {LitElement, PropertyValues, css, html} from 'lit';
 import {customElement, query, property, state} from 'lit/decorators.js';
 import {assertIsDefined} from '../../../utils/common-util';
-import {createEditUrl} from '../../../models/views/edit';
+import {createEditUrl} from '../../../models/views/change';
 import {resolve} from '../../../models/dependency';
 import {modalStyles} from '../../../styles/gr-modal-styles';
 import {GrCreateFileEditDialog} from '../gr-create-change-dialog/gr-create-file-edit-dialog';
@@ -320,8 +320,8 @@
           createEditUrl({
             changeNum: change._number,
             repo: change.project,
-            path: CONFIG_PATH,
             patchNum: INITIAL_PATCHSET,
+            editView: {path: CONFIG_PATH},
           })
         );
       })
diff --git a/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions.ts b/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions.ts
index 75854cc..e47b450 100644
--- a/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions.ts
+++ b/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions.ts
@@ -1577,10 +1577,11 @@
       base: e.detail.base,
       allow_conflicts: e.detail.allowConflicts,
     };
+    const rebaseChain = !!e.detail.rebaseChain;
     this.fireAction(
-      '/rebase',
+      rebaseChain ? '/rebase:chain' : '/rebase',
       assertUIActionInfo(this.revisionActions.rebase),
-      true,
+      rebaseChain ? false : true,
       payload,
       {allow_conflicts: payload.allow_conflicts}
     );
diff --git a/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions_test.ts b/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions_test.ts
index c6bfd55..4602eac 100644
--- a/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions_test.ts
+++ b/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions_test.ts
@@ -625,7 +625,9 @@
       };
       assert.isTrue(fetchChangesStub.called);
       element.handleRebaseConfirm(
-        new CustomEvent('', {detail: {base: '1234', allowConflicts: false}})
+        new CustomEvent('', {
+          detail: {base: '1234', allowConflicts: false, rebaseChain: false},
+        })
       );
       assert.deepEqual(fireActionStub.lastCall.args, [
         '/rebase',
diff --git a/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view.ts b/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view.ts
index 8cbef27..c0ed3b3 100644
--- a/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view.ts
+++ b/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view.ts
@@ -135,10 +135,6 @@
   fireTitleChange,
 } from '../../../utils/event-util';
 import {
-  GerritView,
-  routerModelToken,
-} from '../../../services/router/router-model';
-import {
   debounce,
   DelayedTask,
   throttleWrap,
@@ -176,12 +172,13 @@
 import {getBaseUrl, prependOrigin} from '../../../utils/url-util';
 import {CopyLink, GrCopyLinks} from '../gr-copy-links/gr-copy-links';
 import {
+  ChangeChildView,
   changeViewModelToken,
   ChangeViewState,
   createChangeUrl,
+  createEditUrl,
 } from '../../../models/views/change';
 import {rootUrl} from '../../../utils/url-util';
-import {createEditUrl} from '../../../models/views/edit';
 import {userModelToken} from '../../../models/user/user-model';
 import {pluginLoaderToken} from '../../shared/gr-js-api-interface/gr-plugin-loader';
 import {modalStyles} from '../../../styles/gr-modal-styles';
@@ -539,8 +536,6 @@
 
   private readonly getChangeModel = resolve(this, changeModelToken);
 
-  private readonly getRouterModel = resolve(this, routerModelToken);
-
   private readonly getCommentsModel = resolve(this, commentsModelToken);
 
   private readonly getConfigModel = resolve(this, configModelToken);
@@ -573,7 +568,7 @@
 
   /** Simply reflects the router-model value. */
   // visible for testing
-  routerPatchNum?: PatchSetNum;
+  viewModelPatchNum?: PatchSetNum;
 
   private readonly shortcutsController = new ShortcutController(this);
 
@@ -700,16 +695,16 @@
     );
     subscribe(
       this,
-      () => this.getRouterModel().routerView$,
-      view => {
-        this.isViewCurrent = view === GerritView.CHANGE;
+      () => this.getViewModel().childView$,
+      childView => {
+        this.isViewCurrent = childView === ChangeChildView.OVERVIEW;
       }
     );
     subscribe(
       this,
-      () => this.getRouterModel().routerPatchNum$,
+      () => this.getViewModel().patchNum$,
       patchNum => {
-        this.routerPatchNum = patchNum;
+        this.viewModelPatchNum = patchNum;
       }
     );
     subscribe(
@@ -1531,7 +1526,6 @@
           .allPatchSets=${this.allPatchSets}
           .change=${this.change}
           .changeNum=${this.changeNum}
-          .revisionInfo=${this.getRevisionInfo()}
           .commitInfo=${this.commitInfo}
           .changeUrl=${this.computeChangeUrl()}
           .editMode=${this.getEditMode()}
@@ -2092,13 +2086,6 @@
       return;
     }
 
-    if (this.viewState.changeNum && this.viewState.repo) {
-      this.restApiService.setInProjectLookup(
-        this.viewState.changeNum,
-        this.viewState.repo
-      );
-    }
-
     if (this.viewState.basePatchNum === undefined)
       this.viewState.basePatchNum = PARENT;
 
@@ -2448,6 +2435,7 @@
 
   // Private but used in tests.
   handleDiffBaseAgainstLeft() {
+    if (this.viewState?.childView !== ChangeChildView.OVERVIEW) return;
     assertIsDefined(this.change, 'change');
     assertIsDefined(this.patchRange, 'patchRange');
 
@@ -2650,7 +2638,7 @@
     // is under change-model control. `patchRange.patchNum` should eventually
     // also be model managed, so we can reconcile these two code snippets into
     // one location.
-    if (!this.routerPatchNum && latestPsNum === editParentRev._number) {
+    if (!this.viewModelPatchNum && latestPsNum === editParentRev._number) {
       this.patchRange = {...this.patchRange, patchNum: EDIT};
       // The file list is not reactive (yet) with regards to patch range
       // changes, so we have to actively trigger it.
@@ -3143,8 +3131,8 @@
           createEditUrl({
             changeNum: this.change._number,
             repo: this.change.project,
-            path,
             patchNum: this.patchRange.patchNum,
+            editView: {path},
           })
         );
         break;
diff --git a/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view_test.ts b/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view_test.ts
index 9d89192..9b78e64 100644
--- a/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view_test.ts
+++ b/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view_test.ts
@@ -99,7 +99,7 @@
 import {Modifier} from '../../../utils/dom-util';
 import {GrButton} from '../../shared/gr-button/gr-button';
 import {GrCopyLinks} from '../gr-copy-links/gr-copy-links';
-import {ChangeViewState} from '../../../models/views/change';
+import {ChangeChildView, ChangeViewState} from '../../../models/views/change';
 import {rootUrl} from '../../../utils/url-util';
 import {testResolver} from '../../../test/common-test-setup';
 import {UserModel, userModelToken} from '../../../models/user/user-model';
@@ -369,6 +369,7 @@
     );
     element.viewState = {
       view: GerritView.CHANGE,
+      childView: ChangeChildView.OVERVIEW,
       changeNum: TEST_NUMERIC_CHANGE_ID,
       repo: 'gerrit' as RepoName,
     };
@@ -1986,7 +1987,7 @@
 
     // When edit is set, but patchNum as well, then keep patchNum.
     element.patchRange.patchNum = 5 as RevisionPatchSetNum;
-    element.routerPatchNum = 5 as RevisionPatchSetNum;
+    element.viewModelPatchNum = 5 as RevisionPatchSetNum;
     element.processEdit(change);
     assert.equal(element.patchRange.patchNum, 5 as RevisionPatchSetNum);
   });
diff --git a/polygerrit-ui/app/elements/change/gr-confirm-rebase-dialog/gr-confirm-rebase-dialog.ts b/polygerrit-ui/app/elements/change/gr-confirm-rebase-dialog/gr-confirm-rebase-dialog.ts
index da61b60..b0dbda5 100644
--- a/polygerrit-ui/app/elements/change/gr-confirm-rebase-dialog/gr-confirm-rebase-dialog.ts
+++ b/polygerrit-ui/app/elements/change/gr-confirm-rebase-dialog/gr-confirm-rebase-dialog.ts
@@ -5,6 +5,7 @@
  */
 import {css, html, LitElement, PropertyValues} from 'lit';
 import {customElement, property, query, state} from 'lit/decorators.js';
+import {when} from 'lit/directives/when.js';
 import {
   NumericChangeId,
   BranchName,
@@ -21,6 +22,7 @@
 import {sharedStyles} from '../../../styles/shared-styles';
 import {ValueChangedEvent} from '../../../types/events';
 import {throwingErrorCallback} from '../../shared/gr-rest-api-interface/gr-rest-apis/gr-rest-api-helper';
+import {KnownExperimentId} from '../../../services/flags/flags';
 
 export interface RebaseChange {
   name: string;
@@ -30,6 +32,7 @@
 export interface ConfirmRebaseEventDetail {
   base: string | null;
   allowConflicts: boolean;
+  rebaseChain: boolean;
 }
 
 @customElement('gr-confirm-rebase-dialog')
@@ -85,11 +88,16 @@
   @query('#rebaseAllowConflicts')
   private rebaseAllowConflicts!: HTMLInputElement;
 
+  @query('#rebaseChain')
+  private rebaseChain?: HTMLInputElement;
+
   @query('#parentInput')
   parentInput!: GrAutocomplete;
 
   private readonly restApiService = getAppContext().restApiService;
 
+  private readonly flagsService = getAppContext().flagsService;
+
   constructor() {
     super();
     this.query = input => this.getChangeSuggestions(input);
@@ -221,6 +229,14 @@
               >Allow rebase with conflicts</label
             >
           </div>
+          ${when(
+            this.flagsService.isEnabled(KnownExperimentId.REBASE_CHAIN),
+            () =>
+              html`<div>
+                <input id="rebaseChain" type="checkbox" />
+                <label for="rebaseChain">Rebase all ancestors</label>
+              </div>`
+          )}
         </div>
       </gr-dialog>
     `;
@@ -326,6 +342,7 @@
     const detail: ConfirmRebaseEventDetail = {
       base: this.getSelectedBase(),
       allowConflicts: this.rebaseAllowConflicts.checked,
+      rebaseChain: !!this.rebaseChain?.checked,
     };
     this.dispatchEvent(new CustomEvent('confirm', {detail}));
     this.text = '';
diff --git a/polygerrit-ui/app/elements/change/gr-file-list-header/gr-file-list-header.ts b/polygerrit-ui/app/elements/change/gr-file-list-header/gr-file-list-header.ts
index 89a1ff5..c1e866c 100644
--- a/polygerrit-ui/app/elements/change/gr-file-list-header/gr-file-list-header.ts
+++ b/polygerrit-ui/app/elements/change/gr-file-list-header/gr-file-list-header.ts
@@ -20,8 +20,6 @@
   PatchSetNum,
   CommitInfo,
   ServerInfo,
-  RevisionInfo,
-  NumericChangeId,
   BasePatchSetNum,
 } from '../../../types/common';
 import {DiffPreferencesInfo} from '../../../types/diff';
@@ -71,9 +69,6 @@
   change: ChangeInfo | undefined;
 
   @property({type: String})
-  changeNum?: NumericChangeId;
-
-  @property({type: String})
   changeUrl?: string;
 
   @property({type: Object})
@@ -97,9 +92,6 @@
   @property({type: String})
   filesExpanded?: FilesExpandedState;
 
-  @property({type: Object})
-  revisionInfo?: RevisionInfo;
-
   @state()
   diffPrefs?: DiffPreferencesInfo;
 
@@ -274,12 +266,6 @@
           <div class="patchInfoContent">
             <gr-patch-range-select
               id="rangeSelect"
-              .changeNum=${this.changeNum}
-              .patchNum=${this.patchNum}
-              .basePatchNum=${this.basePatchNum}
-              .availablePatches=${this.allPatchSets}
-              .revisions=${this.change.revisions}
-              .revisionInfo=${this.revisionInfo}
               @patch-range-change=${this.handlePatchChange}
             >
             </gr-patch-range-select>
diff --git a/polygerrit-ui/app/elements/change/gr-file-list-header/gr-file-list-header_test.ts b/polygerrit-ui/app/elements/change/gr-file-list-header/gr-file-list-header_test.ts
index 23534a0..6c2282b 100644
--- a/polygerrit-ui/app/elements/change/gr-file-list-header/gr-file-list-header_test.ts
+++ b/polygerrit-ui/app/elements/change/gr-file-list-header/gr-file-list-header_test.ts
@@ -18,7 +18,6 @@
 import {
   BasePatchSetNum,
   ChangeId,
-  NumericChangeId,
   PARENT,
   PatchSetNum,
   PatchSetNumber,
@@ -174,7 +173,6 @@
   });
 
   test('show/hide diffs disabled for large amounts of files', async () => {
-    element.changeNum = 42 as NumericChangeId;
     element.basePatchNum = PARENT;
     element.patchNum = '2' as PatchSetNum;
     element.shownFileCount = 1;
diff --git a/polygerrit-ui/app/elements/change/gr-file-list/gr-file-list.ts b/polygerrit-ui/app/elements/change/gr-file-list/gr-file-list.ts
index 071c489..d4defcb 100644
--- a/polygerrit-ui/app/elements/change/gr-file-list/gr-file-list.ts
+++ b/polygerrit-ui/app/elements/change/gr-file-list/gr-file-list.ts
@@ -78,9 +78,11 @@
 import {incrementalRepeat} from '../../lit/incremental-repeat';
 import {ifDefined} from 'lit/directives/if-defined.js';
 import {HtmlPatched} from '../../../utils/lit-util';
-import {createDiffUrl} from '../../../models/views/diff';
-import {createEditUrl} from '../../../models/views/edit';
-import {createChangeUrl} from '../../../models/views/change';
+import {
+  createDiffUrl,
+  createEditUrl,
+  createChangeUrl,
+} from '../../../models/views/change';
 import {userModelToken} from '../../../models/user/user-model';
 import {pluginLoaderToken} from '../../shared/gr-js-api-interface/gr-plugin-loader';
 import {FileMode, fileModeToString} from '../../../utils/file-util';
@@ -758,7 +760,7 @@
     );
     subscribe(
       this,
-      () => this.getFilesModel().filesWithUnmodified$,
+      () => this.getFilesModel().filesIncludingUnmodified$,
       files => {
         this.files = [...files];
       }
@@ -2121,9 +2123,9 @@
     this.getNavigation().setUrl(
       createDiffUrl({
         change: this.change,
-        path: diff.path,
         patchNum: this.patchRange.patchNum,
         basePatchNum: this.patchRange.basePatchNum,
+        diffView: {path: diff.path},
       })
     );
   }
@@ -2142,9 +2144,9 @@
     this.getNavigation().setUrl(
       createDiffUrl({
         change: this.change,
-        path: this.files[this.fileCursor.index].__path,
         patchNum: this.patchRange.patchNum,
         basePatchNum: this.patchRange.basePatchNum,
+        diffView: {path: this.files[this.fileCursor.index].__path},
       })
     );
   }
@@ -2176,16 +2178,16 @@
       return createEditUrl({
         changeNum: this.change._number,
         repo: this.change.project,
-        path,
         patchNum: this.patchRange.patchNum,
+        editView: {path},
       });
     }
     return createDiffUrl({
       changeNum: this.change._number,
       repo: this.change.project,
-      path,
       patchNum: this.patchRange.patchNum,
       basePatchNum: this.patchRange.basePatchNum,
+      diffView: {path},
     });
   }
 
diff --git a/polygerrit-ui/app/elements/checks/gr-checks-results.ts b/polygerrit-ui/app/elements/checks/gr-checks-results.ts
index 3fdb1c0..5792230 100644
--- a/polygerrit-ui/app/elements/checks/gr-checks-results.ts
+++ b/polygerrit-ui/app/elements/checks/gr-checks-results.ts
@@ -75,8 +75,7 @@
 import {HtmlPatched} from '../../utils/lit-util';
 import {DropdownItem} from '../shared/gr-dropdown-list/gr-dropdown-list';
 import './gr-checks-attempt';
-import {createDiffUrl} from '../../models/views/diff';
-import {changeViewModelToken} from '../../models/views/change';
+import {createDiffUrl, changeViewModelToken} from '../../models/views/change';
 
 /**
  * Firing this event sets the regular expression of the results filter.
@@ -715,9 +714,8 @@
         url: createDiffUrl({
           changeNum: change._number,
           repo: change.project,
-          path,
           patchNum: patchset,
-          lineNum: line,
+          diffView: {path, lineNum: line},
         }),
         primary: true,
       };
diff --git a/polygerrit-ui/app/elements/core/gr-main-header/gr-main-header.ts b/polygerrit-ui/app/elements/core/gr-main-header/gr-main-header.ts
index b1ff749..833a91a 100644
--- a/polygerrit-ui/app/elements/core/gr-main-header/gr-main-header.ts
+++ b/polygerrit-ui/app/elements/core/gr-main-header/gr-main-header.ts
@@ -219,6 +219,7 @@
         }
         .titleText::after {
           content: var(--header-title-content);
+          white-space: nowrap;
         }
         ul {
           list-style: none;
diff --git a/polygerrit-ui/app/elements/core/gr-router/gr-router.ts b/polygerrit-ui/app/elements/core/gr-router/gr-router.ts
index 1b914bf..bcf6937 100644
--- a/polygerrit-ui/app/elements/core/gr-router/gr-router.ts
+++ b/polygerrit-ui/app/elements/core/gr-router/gr-router.ts
@@ -10,7 +10,11 @@
 } from '../../../utils/page-wrapper-utils';
 import {NavigationService} from '../gr-navigation/gr-navigation';
 import {getAppContext} from '../../../services/app-context';
-import {convertToPatchSetNum} from '../../../utils/patch-set-util';
+import {
+  computeAllPatchSets,
+  computeLatestPatchNum,
+  convertToPatchSetNum,
+} from '../../../utils/patch-set-util';
 import {assertIsDefined} from '../../../utils/common-util';
 import {
   BasePatchSetNum,
@@ -27,7 +31,7 @@
 import {AppElement, AppElementParams} from '../../gr-app-types';
 import {LocationChangeEventDetail} from '../../../types/events';
 import {GerritView, RouterModel} from '../../../services/router/router-model';
-import {firePageError} from '../../../utils/event-util';
+import {fireAlert, firePageError} from '../../../utils/event-util';
 import {windowLocationReload} from '../../../utils/dom-util';
 import {
   getBaseUrl,
@@ -61,13 +65,13 @@
   GroupViewModel,
   GroupViewState,
 } from '../../../models/views/group';
-import {DiffViewModel, DiffViewState} from '../../../models/views/diff';
 import {
+  ChangeChildView,
   ChangeViewModel,
   ChangeViewState,
-  createChangeUrl,
+  createChangeViewUrl,
+  createDiffUrl,
 } from '../../../models/views/change';
-import {EditViewModel, EditViewState} from '../../../models/views/edit';
 import {
   DashboardViewModel,
   DashboardViewState,
@@ -88,6 +92,13 @@
 import {SearchViewModel, SearchViewState} from '../../../models/views/search';
 import {DashboardSection} from '../../../utils/dashboard-util';
 import {Subscription} from 'rxjs';
+import {
+  addPath,
+  findComment,
+  getPatchRangeForCommentUrl,
+  isInBaseOfPatchRange,
+} from '../../../utils/comment-util';
+import {isFileUnchanged} from '../../../embed/diff/gr-diff/gr-diff-utils';
 
 const RoutePattern = {
   ROOT: '/',
@@ -303,9 +314,7 @@
     private readonly agreementViewModel: AgreementViewModel,
     private readonly changeViewModel: ChangeViewModel,
     private readonly dashboardViewModel: DashboardViewModel,
-    private readonly diffViewModel: DiffViewModel,
     private readonly documentationViewModel: DocumentationViewModel,
-    private readonly editViewModel: EditViewModel,
     private readonly groupViewModel: GroupViewModel,
     private readonly pluginViewModel: PluginViewModel,
     private readonly repoViewModel: RepoViewModel,
@@ -322,7 +331,7 @@
         // So this check is slightly fragile, but should work.
         if (this.view !== GerritView.CHANGE) return;
         const browserUrl = new URL(window.location.toString());
-        const stateUrl = new URL(createChangeUrl(state), browserUrl);
+        const stateUrl = new URL(createChangeViewUrl(state), browserUrl);
 
         // Keeping the hash and certain parameters are stop-gap solution. We
         // should find better ways of maintaining an overall consistent URL
@@ -363,13 +372,14 @@
     if ('repo' in state && state.repo !== undefined && 'changeNum' in state)
       this.restApiService.setInProjectLookup(state.changeNum, state.repo);
 
-    this.routerModel.setState({
-      view: state.view,
-      changeNum: 'changeNum' in state ? state.changeNum : undefined,
-      patchNum: 'patchNum' in state ? state.patchNum ?? undefined : undefined,
-      basePatchNum:
-        'basePatchNum' in state ? state.basePatchNum ?? undefined : undefined,
-    });
+    this.routerModel.setState({view: state.view});
+    // We are trying to reset the change (view) model when navigating to other
+    // views, because we don't trust our reset logic at the moment. The models
+    // singletons and might unintentionally keep state from one change to
+    // another. TODO: Let's find some way to avoid that.
+    if (state.view !== GerritView.CHANGE) {
+      this.changeViewModel.setState(undefined);
+    }
     this.appElement().params = state;
   }
 
@@ -1441,6 +1451,7 @@
       basePatchNum: convertToPatchSetNum(ctx.params[4]) as BasePatchSetNum,
       patchNum: convertToPatchSetNum(ctx.params[6]) as RevisionPatchSetNum,
       view: GerritView.CHANGE,
+      childView: ChangeChildView.OVERVIEW,
     };
 
     const queryMap = new URLSearchParams(ctx.querystring);
@@ -1471,21 +1482,57 @@
     this.changeViewModel.setState(state);
   }
 
-  handleCommentRoute(ctx: PageContext) {
+  async handleCommentRoute(ctx: PageContext) {
     const changeNum = Number(ctx.params[1]) as NumericChangeId;
-    const state: DiffViewState = {
-      repo: ctx.params[0] as RepoName,
+    const repo = ctx.params[0] as RepoName;
+    const commentId = ctx.params[2] as UrlEncodedCommentId;
+
+    const comments = await this.restApiService.getDiffComments(changeNum);
+    const change = await this.restApiService.getChangeDetail(changeNum);
+
+    const comment = findComment(addPath(comments), commentId);
+    const path = comment?.path;
+    const patchsets = computeAllPatchSets(change);
+    const latestPatchNum = computeLatestPatchNum(patchsets);
+    if (!comment || !path || !latestPatchNum) {
+      this.show404();
+      return;
+    }
+    let {basePatchNum, patchNum} = getPatchRangeForCommentUrl(
+      comment,
+      latestPatchNum
+    );
+
+    if (basePatchNum !== PARENT) {
+      const diff = await this.restApiService.getDiff(
+        changeNum,
+        basePatchNum,
+        patchNum,
+        path
+      );
+      if (diff && isFileUnchanged(diff)) {
+        fireAlert(
+          document,
+          `File is unchanged between Patchset ${basePatchNum} and ${patchNum}.
+           Showing diff of Base vs ${basePatchNum}.`
+        );
+        patchNum = basePatchNum as RevisionPatchSetNum;
+        basePatchNum = PARENT;
+      }
+    }
+
+    const diffUrl = createDiffUrl({
       changeNum,
-      commentId: ctx.params[2] as UrlEncodedCommentId,
-      view: GerritView.DIFF,
-      commentLink: true,
-    };
-    this.reporting.setRepoName(state.repo ?? '');
-    this.reporting.setChangeId(changeNum);
-    this.normalizePatchRangeParams(state);
-    // Note that router model view must be updated before view models.
-    this.setState(state);
-    this.diffViewModel.setState(state);
+      repo,
+      patchNum,
+      basePatchNum,
+      diffView: {
+        path,
+        lineNum: comment.line,
+        leftSide: isInBaseOfPatchRange(comment, {basePatchNum, patchNum}),
+      },
+    });
+    this.redirect(diffUrl);
   }
 
   handleCommentsRoute(ctx: PageContext) {
@@ -1495,6 +1542,7 @@
       changeNum,
       commentId: ctx.params[2] as UrlEncodedCommentId,
       view: GerritView.CHANGE,
+      childView: ChangeChildView.OVERVIEW,
     };
     assertIsDefined(state.repo);
     this.reporting.setRepoName(state.repo);
@@ -1508,25 +1556,26 @@
   handleDiffRoute(ctx: PageContext) {
     const changeNum = Number(ctx.params[1]) as NumericChangeId;
     // Parameter order is based on the regex group number matched.
-    const state: DiffViewState = {
+    const state: ChangeViewState = {
       repo: ctx.params[0] as RepoName,
       changeNum,
       basePatchNum: convertToPatchSetNum(ctx.params[4]) as BasePatchSetNum,
       patchNum: convertToPatchSetNum(ctx.params[6]) as RevisionPatchSetNum,
-      path: ctx.params[8],
-      view: GerritView.DIFF,
+      view: GerritView.CHANGE,
+      childView: ChangeChildView.DIFF,
+      diffView: {path: ctx.params[8]},
     };
     const address = this.parseLineAddress(ctx.hash);
     if (address) {
-      state.leftSide = address.leftSide;
-      state.lineNum = address.lineNum;
+      state.diffView!.leftSide = address.leftSide;
+      state.diffView!.lineNum = address.lineNum;
     }
     this.reporting.setRepoName(state.repo ?? '');
     this.reporting.setChangeId(changeNum);
     this.normalizePatchRangeParams(state);
     // Note that router model view must be updated before view models.
     this.setState(state);
-    this.diffViewModel.setState(state);
+    this.changeViewModel.setState(state);
   }
 
   handleChangeLegacyRoute(ctx: PageContext) {
@@ -1554,19 +1603,19 @@
     // Parameter order is based on the regex group number matched.
     const project = ctx.params[0] as RepoName;
     const changeNum = Number(ctx.params[1]) as NumericChangeId;
-    const state: EditViewState = {
+    const state: ChangeViewState = {
       repo: project,
       changeNum,
       // for edit view params, patchNum cannot be undefined
       patchNum: convertToPatchSetNum(ctx.params[2]) as RevisionPatchSetNum,
-      path: ctx.params[3],
-      lineNum: Number(ctx.hash),
-      view: GerritView.EDIT,
+      view: GerritView.CHANGE,
+      childView: ChangeChildView.EDIT,
+      editView: {path: ctx.params[3], lineNum: Number(ctx.hash)},
     };
     this.normalizePatchRangeParams(state);
     // Note that router model view must be updated before view models.
     this.setState(state);
-    this.editViewModel.setState(state);
+    this.changeViewModel.setState(state);
     this.reporting.setRepoName(project);
     this.reporting.setChangeId(changeNum);
   }
@@ -1581,6 +1630,7 @@
       changeNum,
       patchNum: convertToPatchSetNum(ctx.params[3]) as RevisionPatchSetNum,
       view: GerritView.CHANGE,
+      childView: ChangeChildView.OVERVIEW,
       edit: true,
     };
     const tab = queryMap.get('tab');
diff --git a/polygerrit-ui/app/elements/core/gr-router/gr-router_test.ts b/polygerrit-ui/app/elements/core/gr-router/gr-router_test.ts
index b8f68e6..d8761bf 100644
--- a/polygerrit-ui/app/elements/core/gr-router/gr-router_test.ts
+++ b/polygerrit-ui/app/elements/core/gr-router/gr-router_test.ts
@@ -28,10 +28,16 @@
 import {AdminChildView} from '../../../models/views/admin';
 import {RepoDetailView} from '../../../models/views/repo';
 import {GroupDetailView} from '../../../models/views/group';
-import {EditViewState} from '../../../models/views/edit';
-import {ChangeViewState} from '../../../models/views/change';
+import {ChangeChildView, ChangeViewState} from '../../../models/views/change';
 import {PatchRangeParams} from '../../../utils/url-util';
 import {testResolver} from '../../../test/common-test-setup';
+import {
+  createComment,
+  createDiff,
+  createParsedChange,
+  createRevision,
+} from '../../../test/test-data-generators';
+import {ParsedChangeInfo} from '../../../types/types';
 
 suite('gr-router tests', () => {
   let router: GrRouter;
@@ -1134,6 +1140,7 @@
           const ctx = makeParams('', '');
           assertctxToParams(ctx, 'handleChangeRoute', {
             view: GerritView.CHANGE,
+            childView: ChangeChildView.OVERVIEW,
             repo: 'foo/bar' as RepoName,
             changeNum: 1234 as NumericChangeId,
             basePatchNum: 4 as BasePatchSetNum,
@@ -1154,6 +1161,7 @@
           ctx.querystring = queryMap.toString();
           assertctxToParams(ctx, 'handleChangeRoute', {
             view: GerritView.CHANGE,
+            childView: ChangeChildView.OVERVIEW,
             repo: 'foo/bar' as RepoName,
             changeNum: 1234 as NumericChangeId,
             basePatchNum: 4 as BasePatchSetNum,
@@ -1193,36 +1201,89 @@
         test('diff view', () => {
           const ctx = makeParams('foo/bar/baz', 'b44');
           assertctxToParams(ctx, 'handleDiffRoute', {
-            view: GerritView.DIFF,
+            view: GerritView.CHANGE,
+            childView: ChangeChildView.DIFF,
             repo: 'foo/bar' as RepoName,
             changeNum: 1234 as NumericChangeId,
             basePatchNum: 4 as BasePatchSetNum,
             patchNum: 7 as RevisionPatchSetNum,
-            path: 'foo/bar/baz',
-            leftSide: true,
-            lineNum: 44,
+            diffView: {
+              path: 'foo/bar/baz',
+              lineNum: 44,
+              leftSide: true,
+            },
           });
           assert.isFalse(redirectStub.called);
         });
 
-        test('comment route', () => {
-          const url = '/c/gerrit/+/264833/comment/00049681_f34fd6a9/';
+        test('comment route base..1', async () => {
+          const change: ParsedChangeInfo = createParsedChange();
+          const repo = change.project;
+          const changeNum = change._number;
+          const ps = 1 as RevisionPatchSetNum;
+          const line = 23;
+          const id = '00049681_f34fd6a9' as UrlEncodedCommentId;
+          stubRestApi('getChangeDetail').resolves(change);
+          stubRestApi('getDiffComments').resolves({
+            filepath: [{...createComment(), id, patch_set: ps, line}],
+          });
+
+          const url = `/c/${repo}/+/${changeNum}/comment/${id}/`;
           const groups = url.match(_testOnly_RoutePattern.COMMENT);
-          assert.deepEqual(groups!.slice(1), [
-            'gerrit', // project
-            '264833', // changeNum
-            '00049681_f34fd6a9', // commentId
-          ]);
-          assertctxToParams(
-            {params: groups!.slice(1)} as any,
-            'handleCommentRoute',
-            {
-              repo: 'gerrit' as RepoName,
-              changeNum: 264833 as NumericChangeId,
-              commentId: '00049681_f34fd6a9' as UrlEncodedCommentId,
-              commentLink: true,
-              view: GerritView.DIFF,
-            }
+          assert.deepEqual(groups!.slice(1), [repo, `${changeNum}`, id]);
+
+          await router.handleCommentRoute({params: groups!.slice(1)} as any);
+          assert.isTrue(redirectStub.calledOnce);
+          assert.equal(
+            redirectStub.lastCall.args[0],
+            `/c/${repo}/+/${changeNum}/${ps}/filepath#${line}`
+          );
+        });
+
+        test('comment route 1..2', async () => {
+          const change: ParsedChangeInfo = {
+            ...createParsedChange(),
+            revisions: {
+              abc: createRevision(1),
+              def: createRevision(2),
+            },
+          };
+          const repo = change.project;
+          const changeNum = change._number;
+          const ps = 1 as RevisionPatchSetNum;
+          const line = 23;
+          const id = '00049681_f34fd6a9' as UrlEncodedCommentId;
+
+          stubRestApi('getChangeDetail').resolves(change);
+          stubRestApi('getDiffComments').resolves({
+            filepath: [{...createComment(), id, patch_set: ps, line}],
+          });
+          const diffStub = stubRestApi('getDiff');
+
+          const url = `/c/${repo}/+/${changeNum}/comment/${id}/`;
+          const groups = url.match(_testOnly_RoutePattern.COMMENT);
+
+          // If getDiff() returns a diff with changes, then we will compare
+          // the patchset of the comment (1) against latest (2).
+          diffStub.onFirstCall().resolves(createDiff());
+          await router.handleCommentRoute({params: groups!.slice(1)} as any);
+          assert.isTrue(redirectStub.calledOnce);
+          assert.equal(
+            redirectStub.lastCall.args[0],
+            `/c/${repo}/+/${changeNum}/${ps}..2/filepath#b${line}`
+          );
+
+          // If getDiff() returns an unchanged diff, then we will compare
+          // the patchset of the comment (1) against base.
+          diffStub.onSecondCall().resolves({
+            ...createDiff(),
+            content: [],
+          });
+          await router.handleCommentRoute({params: groups!.slice(1)} as any);
+          assert.isTrue(redirectStub.calledTwice);
+          assert.equal(
+            redirectStub.lastCall.args[0],
+            `/c/${repo}/+/${changeNum}/${ps}/filepath#${line}`
           );
         });
 
@@ -1242,6 +1303,7 @@
               changeNum: 264833 as NumericChangeId,
               commentId: '00049681_f34fd6a9' as UrlEncodedCommentId,
               view: GerritView.CHANGE,
+              childView: ChangeChildView.OVERVIEW,
             }
           );
         });
@@ -1259,13 +1321,13 @@
             3: 'foo/bar/baz', // 3 File path
           },
         };
-        const appParams: EditViewState = {
+        const appParams: ChangeViewState = {
           repo: 'foo/bar' as RepoName,
           changeNum: 1234 as NumericChangeId,
-          view: GerritView.EDIT,
-          path: 'foo/bar/baz',
+          view: GerritView.CHANGE,
+          childView: ChangeChildView.EDIT,
           patchNum: 3 as RevisionPatchSetNum,
-          lineNum: 0,
+          editView: {path: 'foo/bar/baz', lineNum: 0},
         };
 
         router.handleDiffEditRoute(ctx);
@@ -1285,13 +1347,13 @@
             3: 'foo/bar/baz', // 3 File path
           },
         };
-        const appParams: EditViewState = {
+        const appParams: ChangeViewState = {
           repo: 'foo/bar' as RepoName,
           changeNum: 1234 as NumericChangeId,
-          view: GerritView.EDIT,
-          path: 'foo/bar/baz',
+          view: GerritView.CHANGE,
+          childView: ChangeChildView.EDIT,
           patchNum: 3 as RevisionPatchSetNum,
-          lineNum: 4,
+          editView: {path: 'foo/bar/baz', lineNum: 4},
         };
 
         router.handleDiffEditRoute(ctx);
@@ -1314,6 +1376,7 @@
           repo: 'foo/bar' as RepoName,
           changeNum: 1234 as NumericChangeId,
           view: GerritView.CHANGE,
+          childView: ChangeChildView.OVERVIEW,
           patchNum: 3 as RevisionPatchSetNum,
           edit: true,
         };
diff --git a/polygerrit-ui/app/elements/diff/gr-comment-api/gr-comment-api.ts b/polygerrit-ui/app/elements/diff/gr-comment-api/gr-comment-api.ts
index 26043b32..6eb5243 100644
--- a/polygerrit-ui/app/elements/diff/gr-comment-api/gr-comment-api.ts
+++ b/polygerrit-ui/app/elements/diff/gr-comment-api/gr-comment-api.ts
@@ -7,7 +7,6 @@
   PatchRange,
   PatchSetNum,
   RobotCommentInfo,
-  UrlEncodedCommentId,
   PathToCommentsInfoMap,
   FileInfo,
   PARENT,
@@ -64,26 +63,6 @@
     return this._drafts;
   }
 
-  findCommentById(
-    commentId?: UrlEncodedCommentId
-  ): CommentInfo | DraftInfo | undefined {
-    if (!commentId) return undefined;
-    const findComment = (comments: {
-      [path: string]: (CommentInfo | DraftInfo)[];
-    }) => {
-      let comment;
-      for (const path of Object.keys(comments)) {
-        comment = comment || comments[path].find(c => c.id === commentId);
-      }
-      return comment;
-    };
-    return (
-      findComment(this._comments) ||
-      findComment(this._robotComments) ||
-      findComment(this._drafts)
-    );
-  }
-
   /**
    * Get an object mapping file paths to a boolean representing whether that
    * path contains diff comments in the given patch set (including drafts and
diff --git a/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host.ts b/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host.ts
index eb2b494..de92b16 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host.ts
+++ b/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host.ts
@@ -26,12 +26,7 @@
   isInBaseOfPatchRange,
   isInRevisionOfPatchRange,
 } from '../../../utils/comment-util';
-import {
-  CommitRange,
-  CoverageRange,
-  DiffLayer,
-  PatchSetFile,
-} from '../../../types/types';
+import {CoverageRange, DiffLayer, PatchSetFile} from '../../../types/types';
 import {
   Base64ImageFile,
   BlameInfo,
@@ -192,9 +187,6 @@
     fire(this, 'is-image-diff-changed', {value: isImageDiff});
   }
 
-  @property({type: Object})
-  commitRange?: CommitRange;
-
   @state()
   private _editWeblinks?: GeneratedWebLink[];
 
@@ -607,7 +599,11 @@
     this.hasReloadBeenCalledOnce = true;
     this.reporting.time(Timing.DIFF_TOTAL);
     this.reporting.time(Timing.DIFF_LOAD);
+    // TODO: Find better names for these 3 clear/cancel methods. Ideally the
+    // <gr-diff-host> should not re-used at all for another diff rendering pass.
     this.clear();
+    this.cancel();
+    this.clearDiffContent();
     assertIsDefined(this.path, 'path');
     assertIsDefined(this.changeNum, 'changeNum');
     this.diff = undefined;
diff --git a/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view.ts b/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view.ts
index d17c858..a9cbcbd 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view.ts
+++ b/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view.ts
@@ -20,21 +20,12 @@
 import '../gr-diff-preferences-dialog/gr-diff-preferences-dialog';
 import '../gr-patch-range-select/gr-patch-range-select';
 import '../../change/gr-download-dialog/gr-download-dialog';
-import {navigationToken} from '../../core/gr-navigation/gr-navigation';
 import {getAppContext} from '../../../services/app-context';
+import {isMergeParent, getParentIndex} from '../../../utils/patch-set-util';
 import {
-  computeAllPatchSets,
-  computeLatestPatchNum,
-  PatchSet,
-  isMergeParent,
-  getParentIndex,
-} from '../../../utils/patch-set-util';
-import {
-  addUnmodifiedFiles,
   computeDisplayPath,
   computeTruncatedPath,
   isMagicPath,
-  specialFilePathCompare,
 } from '../../../utils/path-list-util';
 import {changeBaseURL, changeIsOpen} from '../../../utils/change-util';
 import {GrDiffHost} from '../../diff/gr-diff-host/gr-diff-host';
@@ -45,52 +36,33 @@
 import {ChangeComments} from '../../diff/gr-comment-api/gr-comment-api';
 import {
   BasePatchSetNum,
-  ChangeInfo,
-  CommitId,
   EDIT,
-  FileInfo,
   NumericChangeId,
   PARENT,
   PatchRange,
-  PatchSetNum,
   PatchSetNumber,
   PreferencesInfo,
   RepoName,
-  RevisionInfo,
   RevisionPatchSetNum,
   ServerInfo,
 } from '../../../types/common';
 import {DiffInfo, DiffPreferencesInfo} from '../../../types/diff';
-import {
-  CommitRange,
-  EditRevisionInfo,
-  FileRange,
-  ParsedChangeInfo,
-} from '../../../types/types';
+import {FileRange, ParsedChangeInfo} from '../../../types/types';
 import {FilesWebLinks} from '../gr-patch-range-select/gr-patch-range-select';
 import {GrDiffCursor} from '../../../embed/diff/gr-diff-cursor/gr-diff-cursor';
 import {CommentSide, DiffViewMode, Side} from '../../../constants/constants';
 import {GrApplyFixDialog} from '../gr-apply-fix-dialog/gr-apply-fix-dialog';
-import {RevisionInfo as RevisionInfoObj} from '../../shared/revision-info/revision-info';
-import {
-  CommentMap,
-  getPatchRangeForCommentUrl,
-  isInBaseOfPatchRange,
-} from '../../../utils/comment-util';
+import {CommentMap} from '../../../utils/comment-util';
 import {
   EventType,
   OpenFixPreviewEvent,
   ValueChangedEvent,
 } from '../../../types/events';
 import {fireAlert, fireEvent, fireTitleChange} from '../../../utils/event-util';
-import {
-  GerritView,
-  routerModelToken,
-} from '../../../services/router/router-model';
 import {assertIsDefined, queryAndAssert} from '../../../utils/common-util';
 import {Key, toggleClass, whenVisible} from '../../../utils/dom-util';
 import {CursorMoveResult} from '../../../api/core';
-import {isFalse, throttleWrap, until} from '../../../utils/async-util';
+import {throttleWrap} from '../../../utils/async-util';
 import {filter, take, switchMap} from 'rxjs/operators';
 import {combineLatest} from 'rxjs';
 import {
@@ -98,14 +70,12 @@
   ShortcutSection,
   shortcutsServiceToken,
 } from '../../../services/shortcuts/shortcuts-service';
-import {LoadingStatus} from '../../../models/change/change-model';
 import {DisplayLine} from '../../../api/diff';
 import {GrDownloadDialog} from '../../change/gr-download-dialog/gr-download-dialog';
 import {commentsModelToken} from '../../../models/comments/comments-model';
 import {changeModelToken} from '../../../models/change/change-model';
 import {resolve} from '../../../models/dependency';
-import {BehaviorSubject} from 'rxjs';
-import {css, html, LitElement, PropertyValues} from 'lit';
+import {css, html, LitElement, nothing, PropertyValues} from 'lit';
 import {ShortcutController} from '../../lit/shortcut-controller';
 import {subscribe} from '../../lit/subscription-controller';
 import {customElement, property, query, state} from 'lit/decorators.js';
@@ -116,16 +86,18 @@
 import {when} from 'lit/directives/when.js';
 import {
   createDiffUrl,
-  diffViewModelToken,
-  DiffViewState,
-} from '../../../models/views/diff';
-import {createChangeUrl} from '../../../models/views/change';
-import {createEditUrl} from '../../../models/views/edit';
+  ChangeChildView,
+  changeViewModelToken,
+} from '../../../models/views/change';
 import {GeneratedWebLink} from '../../../utils/weblink-util';
 import {userModelToken} from '../../../models/user/user-model';
 import {modalStyles} from '../../../styles/gr-modal-styles';
 import {PaperTabsElement} from '@polymer/paper-tabs/paper-tabs';
 import {GrDiffPreferencesDialog} from '../gr-diff-preferences-dialog/gr-diff-preferences-dialog';
+import {
+  FileNameToNormalizedFileInfoMap,
+  filesModelToken,
+} from '../../../models/change/files-model';
 
 const LOADING_BLAME = 'Loading blame...';
 const LOADED_BLAME = 'Blame loaded';
@@ -135,14 +107,11 @@
 
 // visible for testing
 export interface Files {
-  sortedFileList: string[];
-  changeFilesByPath: {[path: string]: FileInfo};
+  /** All file paths sorted by `specialFilePathCompare`. */
+  sortedPaths: string[];
+  changeFilesByPath: FileNameToNormalizedFileInfoMap;
 }
 
-interface CommentSkips {
-  previous: string | null;
-  next: string | null;
-}
 @customElement('gr-diff-view')
 export class GrDiffView extends LitElement {
   /**
@@ -159,8 +128,8 @@
   @query('#diffHost')
   diffHost?: GrDiffHost;
 
-  @query('#reviewed')
-  reviewed?: HTMLInputElement;
+  @state()
+  reviewed = false;
 
   @query('#downloadModal')
   downloadModal?: HTMLDialogElement;
@@ -177,33 +146,31 @@
   @query('#diffPreferencesDialog')
   diffPreferencesDialog?: GrDiffPreferencesDialog;
 
-  private _viewState: DiffViewState | undefined;
-
+  // Private but used in tests.
   @state()
-  get viewState(): DiffViewState | undefined {
-    return this._viewState;
-  }
-
-  set viewState(viewState: DiffViewState | undefined) {
-    if (this._viewState === viewState) return;
-    const oldViewState = this._viewState;
-    this._viewState = viewState;
-    this.viewStateChanged();
-    this.requestUpdate('viewState', oldViewState);
+  get patchRange(): PatchRange | undefined {
+    if (!this.patchNum) return undefined;
+    return {
+      patchNum: this.patchNum,
+      basePatchNum: this.basePatchNum,
+    };
   }
 
   // Private but used in tests.
   @state()
-  patchRange?: PatchRange;
+  patchNum?: RevisionPatchSetNum;
 
   // Private but used in tests.
   @state()
-  commitRange?: CommitRange;
+  basePatchNum: BasePatchSetNum = PARENT;
 
   // Private but used in tests.
   @state()
   change?: ParsedChangeInfo;
 
+  @state()
+  latestPatchNum?: PatchSetNumber;
+
   // Private but used in tests.
   @state()
   changeComments?: ChangeComments;
@@ -216,10 +183,9 @@
   @state()
   diff?: DiffInfo;
 
-  // TODO: Move to using files-model.
   // Private but used in tests.
   @state()
-  files: Files = {sortedFileList: [], changeFilesByPath: {}};
+  files: Files = {sortedPaths: [], changeFilesByPath: {}};
 
   // Private but used in tests
   // Use path getter/setter.
@@ -237,13 +203,13 @@
     this.requestUpdate('path', oldPath);
   }
 
+  /** Allows us to react when the user switches to the DIFF view. */
   // Private but used in tests.
-  @state()
-  loggedIn = false;
+  @state() isActiveChildView = false;
 
   // Private but used in tests.
   @state()
-  loading = true;
+  loggedIn = false;
 
   @property({type: Object})
   prefs?: DiffPreferencesInfo;
@@ -266,65 +232,61 @@
 
   // Private but used in tests.
   @state()
-  commentMap?: CommentMap;
-
-  @state()
-  private commentSkips?: CommentSkips;
-
-  // Private but used in tests.
-  @state()
   isBlameLoaded?: boolean;
 
   @state()
   private isBlameLoading = false;
 
-  @state()
-  private allPatchSets?: PatchSet[] = [];
-
+  /** Directly reflects the view model property `diffView.lineNum`. */
   // Private but used in tests.
   @state()
   focusLineNum?: number;
 
+  /** Directly reflects the view model property `diffView.leftSide`. */
+  @state()
+  leftSide = false;
+
   // visible for testing
   reviewedFiles = new Set<string>();
 
   private readonly reporting = getAppContext().reportingService;
 
-  private readonly restApiService = getAppContext().restApiService;
-
-  private readonly getRouterModel = resolve(this, routerModelToken);
-
   private readonly getUserModel = resolve(this, userModelToken);
 
   private readonly getChangeModel = resolve(this, changeModelToken);
 
   private readonly getCommentsModel = resolve(this, commentsModelToken);
 
+  private readonly getFilesModel = resolve(this, filesModelToken);
+
   private readonly getShortcutsService = resolve(this, shortcutsServiceToken);
 
   private readonly getConfigModel = resolve(this, configModelToken);
 
-  private readonly getViewModel = resolve(this, diffViewModelToken);
+  private readonly getViewModel = resolve(this, changeViewModelToken);
 
   private throttledToggleFileReviewed?: (e: KeyboardEvent) => void;
 
   @state()
   cursor?: GrDiffCursor;
 
-  private connected$ = new BehaviorSubject(false);
-
   private readonly shortcutsController = new ShortcutController(this);
 
-  private readonly getNavigation = resolve(this, navigationToken);
-
   constructor() {
     super();
     this.setupKeyboardShortcuts();
     this.setupSubscriptions();
     subscribe(
       this,
-      () => this.getViewModel().state$,
-      x => (this.viewState = x)
+      () => this.getFilesModel().filesIncludingUnmodified$,
+      files => {
+        const filesByPath: FileNameToNormalizedFileInfoMap = {};
+        for (const f of files) filesByPath[f.__path] = f;
+        this.files = {
+          sortedPaths: files.map(f => f.__path),
+          changeFilesByPath: filesByPath,
+        };
+      }
     );
   }
 
@@ -338,10 +300,10 @@
     listen(Shortcut.PREV_LINE, _ => this.handlePrevLine());
     listen(Shortcut.VISIBLE_LINE, _ => this.cursor?.moveToVisibleArea());
     listen(Shortcut.NEXT_FILE_WITH_COMMENTS, _ =>
-      this.moveToNextFileWithComment()
+      this.moveToFileWithComment(1)
     );
     listen(Shortcut.PREV_FILE_WITH_COMMENTS, _ =>
-      this.moveToPreviousFileWithComment()
+      this.moveToFileWithComment(-1)
     );
     listen(Shortcut.NEW_COMMENT, _ => this.handleNewComment());
     listen(Shortcut.SAVE_COMMENT, _ => {});
@@ -354,7 +316,9 @@
     listen(Shortcut.OPEN_REPLY_DIALOG, _ => this.handleOpenReplyDialog());
     listen(Shortcut.TOGGLE_LEFT_PANE, _ => this.handleToggleLeftPane());
     listen(Shortcut.OPEN_DOWNLOAD_DIALOG, _ => this.handleOpenDownloadDialog());
-    listen(Shortcut.UP_TO_CHANGE, _ => this.handleUpToChange());
+    listen(Shortcut.UP_TO_CHANGE, _ =>
+      this.getChangeModel().navigateToChange()
+    );
     listen(Shortcut.OPEN_DIFF_PREFS, _ => this.handleCommaKey());
     listen(Shortcut.TOGGLE_DIFF_MODE, _ => this.handleToggleDiffMode());
     listen(Shortcut.TOGGLE_FILE_REVIEWED, e => {
@@ -437,6 +401,11 @@
     );
     subscribe(
       this,
+      () => this.getChangeModel().latestPatchNum$,
+      latestPatchNum => (this.latestPatchNum = latestPatchNum)
+    );
+    subscribe(
+      this,
       () => this.getChangeModel().reviewedFiles$,
       reviewedFiles => {
         this.reviewedFiles = new Set(reviewedFiles) ?? new Set();
@@ -444,45 +413,82 @@
     );
     subscribe(
       this,
-      () => this.getChangeModel().diffPath$,
+      () => this.getViewModel().changeNum$,
+      changeNum => {
+        if (!changeNum || this.changeNum === changeNum) return;
+
+        // We are only setting the changeNum of the diff view once!
+        // Everything in the diff view is tied to the change. It seems better to
+        // force the re-creation of the diff view when the change number changes.
+        if (!this.changeNum) {
+          this.changeNum = changeNum;
+        } else {
+          fireEvent(this, EventType.RECREATE_DIFF_VIEW);
+        }
+      }
+    );
+    subscribe(
+      this,
+      () => this.getViewModel().childView$,
+      childView => (this.isActiveChildView = childView === ChangeChildView.DIFF)
+    );
+    subscribe(
+      this,
+      () => this.getViewModel().diffPath$,
       path => (this.path = path)
     );
-
+    subscribe(
+      this,
+      () => this.getViewModel().diffLine$,
+      line => (this.focusLineNum = line)
+    );
+    subscribe(
+      this,
+      () => this.getViewModel().diffLeftSide$,
+      leftSide => (this.leftSide = leftSide)
+    );
+    subscribe(
+      this,
+      () => this.getViewModel().patchNum$,
+      patchNum => (this.patchNum = patchNum)
+    );
+    subscribe(
+      this,
+      () => this.getViewModel().basePatchNum$,
+      basePatchNum => (this.basePatchNum = basePatchNum ?? PARENT)
+    );
     subscribe(
       this,
       () =>
         combineLatest([
-          this.getChangeModel().diffPath$,
+          this.getViewModel().diffPath$,
           this.getChangeModel().reviewedFiles$,
         ]),
       ([path, files]) => {
-        this.updateComplete.then(() => {
-          assertIsDefined(this.reviewed, 'reviewed');
-          this.reviewed.checked = !!path && !!files && files.includes(path);
-        });
+        this.reviewed = !!path && !!files && files.includes(path);
       }
     );
 
-    // When user initially loads the diff view, we want to autmatically mark
+    // When user initially loads the diff view, we want to automatically mark
     // the file as reviewed if they have it enabled. We can't observe these
     // properties since the method will be called anytime a property updates
     // but we only want to call this on the initial load.
     subscribe(
       this,
       () =>
-        this.getChangeModel().diffPath$.pipe(
+        this.getViewModel().diffPath$.pipe(
           filter(diffPath => !!diffPath),
           switchMap(() =>
             combineLatest([
               this.getChangeModel().patchNum$,
-              this.getRouterModel().routerView$,
+              this.getViewModel().childView$,
               this.getUserModel().diffPreferences$,
               this.getChangeModel().reviewedFiles$,
             ]).pipe(
               filter(
-                ([patchNum, routerView, diffPrefs, reviewedFiles]) =>
+                ([patchNum, childView, diffPrefs, reviewedFiles]) =>
                   !!patchNum &&
-                  routerView === GerritView.DIFF &&
+                  childView === ChangeChildView.DIFF &&
                   !!diffPrefs &&
                   !!reviewedFiles
               ),
@@ -491,14 +497,11 @@
           )
         ),
       ([patchNum, _routerView, diffPrefs]) => {
-        this.setReviewedStatus(patchNum!, diffPrefs);
+        // `patchNum` must be defined, because of the `!!patchNum` filter above.
+        assertIsDefined(patchNum, 'patchNum');
+        this.setReviewedStatus(patchNum, diffPrefs);
       }
     );
-    subscribe(
-      this,
-      () => this.getChangeModel().diffPath$,
-      path => (this.path = path)
-    );
   }
 
   static override get styles() {
@@ -691,7 +694,6 @@
 
   override connectedCallback() {
     super.connectedCallback();
-    this.connected$.next(true);
     this.throttledToggleFileReviewed = throttleWrap(_ =>
       this.handleToggleFileReviewed()
     );
@@ -702,38 +704,11 @@
 
   override disconnectedCallback() {
     this.cursor?.dispose();
-    this.connected$.next(false);
     super.disconnectedCallback();
   }
 
-  protected override willUpdate(changedProperties: PropertyValues) {
-    super.willUpdate(changedProperties);
-    if (changedProperties.has('change')) {
-      this.allPatchSets = computeAllPatchSets(this.change);
-    }
-    if (
-      changedProperties.has('commentMap') ||
-      changedProperties.has('files') ||
-      changedProperties.has('path')
-    ) {
-      this.commentSkips = this.computeCommentSkips(
-        this.commentMap,
-        this.files?.sortedFileList,
-        this.path
-      );
-    }
-
-    if (
-      changedProperties.has('changeNum') ||
-      changedProperties.has('changeComments') ||
-      changedProperties.has('patchRange')
-    ) {
-      this.fetchFiles();
-    }
-  }
-
   private reInitCursor() {
-    assertIsDefined(this.diffHost, 'diffHost');
+    if (!this.diffHost) return;
     this.cursor?.replaceDiffs([this.diffHost]);
     this.cursor?.reInitCursor();
   }
@@ -741,16 +716,35 @@
   protected override updated(changedProperties: PropertyValues): void {
     super.updated(changedProperties);
     if (
+      changedProperties.has('change') ||
+      changedProperties.has('path') ||
+      changedProperties.has('patchNum') ||
+      changedProperties.has('basePatchNum')
+    ) {
+      this.reloadDiff();
+    } else if (
+      changedProperties.has('isActiveChildView') &&
+      this.isActiveChildView
+    ) {
+      this.initializePositions();
+    }
+    if (
+      changedProperties.has('focusLineNum') ||
+      changedProperties.has('leftSide')
+    ) {
+      this.initLineOfInterestAndCursor();
+    }
+    if (
+      changedProperties.has('change') ||
       changedProperties.has('changeComments') ||
       changedProperties.has('path') ||
-      changedProperties.has('patchRange') ||
+      changedProperties.has('patchNum') ||
+      changedProperties.has('basePatchNum') ||
       changedProperties.has('files')
     ) {
-      if (this.changeComments && this.path && this.patchRange) {
+      if (this.change && this.changeComments && this.path && this.patchRange) {
         assertIsDefined(this.diffHost, 'diffHost');
-        const file = this.files?.changeFilesByPath
-          ? this.files.changeFilesByPath[this.path]
-          : undefined;
+        const file = this.files?.changeFilesByPath?.[this.path];
         this.diffHost.updateComplete.then(() => {
           assertIsDefined(this.path);
           assertIsDefined(this.patchRange);
@@ -766,17 +760,18 @@
   }
 
   override render() {
+    if (!this.isActiveChildView) return nothing;
+    if (!this.patchNum || !this.changeNum || !this.change || !this.path) {
+      return html`<div class="loading">Loading...</div>`;
+    }
     const file = this.getFileRange();
     return html`
       ${this.renderStickyHeader()}
-      <div class="loading" ?hidden=${!this.loading}>Loading...</div>
       <h2 class="assistive-tech-only">Diff view</h2>
       <gr-diff-host
         id="diffHost"
-        ?hidden=${this.loading}
         .changeNum=${this.changeNum}
         .change=${this.change}
-        .commitRange=${this.commitRange}
         .patchRange=${this.patchRange}
         .file=${file}
         .path=${this.path}
@@ -797,7 +792,7 @@
 
   private renderStickyHeader() {
     return html` <div
-      class="stickyHeader ${this.computeEditMode() ? 'editMode' : ''}"
+      class="stickyHeader ${this.patchNum === EDIT ? 'editMode' : ''}"
     >
       <h1 class="assistive-tech-only">
         Diff of ${this.path ? computeTruncatedPath(this.path) : ''}
@@ -823,7 +818,8 @@
     const fileNum = this.computeFileNum(formattedFiles);
     const fileNumClass = this.computeFileNumClass(fileNum, formattedFiles);
     return html` <div>
-        <a href=${this.getChangePath()}>${this.changeNum}</a
+        <a href=${ifDefined(this.getChangeModel().changeUrl())}
+          >${this.changeNum}</a
         ><span class="changeNumberColon">:</span>
         <span class="headerSubject">${this.change?.subject}</span>
         <input
@@ -833,6 +829,7 @@
           ?hidden=${!this.loggedIn}
           title="Toggle reviewed status of file"
           aria-label="file reviewed"
+          .checked=${this.reviewed}
           @change=${this.handleReviewedChange}
         />
         <div class="jumpToFileContainer">
@@ -866,7 +863,7 @@
             Shortcut.UP_TO_CHANGE,
             ShortcutSection.NAVIGATION
           )}
-          href=${this.getChangePath()}
+          href=${ifDefined(this.getChangeModel().changeUrl())}
           >Up</a
         >
         <span class="separator"></span>
@@ -883,19 +880,10 @@
   }
 
   private renderPatchRangeLeft() {
-    const revisionInfo = this.change
-      ? new RevisionInfoObj(this.change)
-      : undefined;
     return html` <div class="patchRangeLeft">
       <gr-patch-range-select
         id="rangeSelect"
-        .changeNum=${this.changeNum}
-        .patchNum=${this.patchRange?.patchNum}
-        .basePatchNum=${this.patchRange?.basePatchNum}
         .filesWeblinks=${this.filesWeblinks}
-        .availablePatches=${this.allPatchSets}
-        .revisions=${this.change?.revisions}
-        .revisionInfo=${revisionInfo}
         @patch-range-change=${this.handlePatchChange}
       >
       </gr-patch-range-select>
@@ -1022,7 +1010,7 @@
         <gr-download-dialog
           id="downloadDialog"
           .change=${this.change}
-          .patchNum=${this.patchRange?.patchNum}
+          .patchNum=${this.patchNum}
           .config=${this.serverConfig?.download}
           @close=${this.handleDownloadDialogClose}
         ></gr-download-dialog>
@@ -1047,36 +1035,12 @@
     if (!this.files || !this.path) return;
     const fileInfo = this.files.changeFilesByPath[this.path];
     const fileRange: FileRange = {path: this.path};
-    if (fileInfo && fileInfo.old_path) {
+    if (fileInfo?.old_path) {
       fileRange.basePath = fileInfo.old_path;
     }
     return fileRange;
   }
 
-  // Private but used in tests.
-  fetchFiles() {
-    if (!this.changeNum || !this.patchRange || !this.changeComments) {
-      return Promise.resolve();
-    }
-
-    if (!this.patchRange.patchNum) {
-      return Promise.resolve();
-    }
-
-    return this.restApiService
-      .getChangeFiles(this.changeNum, this.patchRange)
-      .then(changeFiles => {
-        if (!changeFiles) return;
-        const commentedPaths = this.changeComments!.getPaths(this.patchRange);
-        const files = {...changeFiles};
-        addUnmodifiedFiles(files, commentedPaths);
-        this.files = {
-          sortedFileList: Object.keys(files).sort(specialFilePathCompare),
-          changeFilesByPath: files,
-        };
-      });
-  }
-
   private handleReviewedChange(e: Event) {
     const input = e.target as HTMLInputElement;
     this.setReviewed(input.checked ?? false);
@@ -1085,12 +1049,14 @@
   // Private but used in tests.
   setReviewed(
     reviewed: boolean,
-    patchNum: RevisionPatchSetNum | undefined = this.patchRange?.patchNum
+    patchNum: RevisionPatchSetNum | undefined = this.patchNum
   ) {
-    if (this.computeEditMode()) return;
+    if (this.patchNum === EDIT) return;
     if (!patchNum || !this.path || !this.changeNum) return;
     // if file is already reviewed then do not make a saveReview request
     if (this.reviewedFiles.has(this.path) && reviewed) return;
+    // optimistic update
+    this.reviewed = reviewed;
     this.getChangeModel().setReviewedFilesStatus(
       this.changeNum,
       patchNum,
@@ -1101,8 +1067,7 @@
 
   // Private but used in tests.
   handleToggleFileReviewed() {
-    assertIsDefined(this.reviewed);
-    this.setReviewed(!this.reviewed.checked);
+    this.setReviewed(!this.reviewed);
   }
 
   private handlePrevLine() {
@@ -1147,48 +1112,13 @@
   }
 
   // Private but used in tests.
-  moveToPreviousFileWithComment() {
-    if (!this.commentSkips) return;
-    if (!this.change) return;
-    if (!this.patchRange?.patchNum) return;
-
-    // If there is no previous diff with comments, then return to the change
-    // view.
-    if (!this.commentSkips.previous) {
-      this.navToChangeView();
-      return;
+  moveToFileWithComment(direction: -1 | 1) {
+    const path = this.findFileWithComment(direction);
+    if (!path) {
+      this.getChangeModel().navigateToChange();
+    } else {
+      this.getChangeModel().navigateToDiff({path});
     }
-
-    this.getNavigation().setUrl(
-      createDiffUrl({
-        change: this.change,
-        path: this.commentSkips.previous,
-        patchNum: this.patchRange.patchNum,
-        basePatchNum: this.patchRange.basePatchNum,
-      })
-    );
-  }
-
-  // Private but used in tests.
-  moveToNextFileWithComment() {
-    if (!this.commentSkips) return;
-    if (!this.change) return;
-    if (!this.patchRange?.patchNum) return;
-
-    // If there is no next diff with comments, then return to the change view.
-    if (!this.commentSkips.next) {
-      this.navToChangeView();
-      return;
-    }
-
-    this.getNavigation().setUrl(
-      createDiffUrl({
-        change: this.change,
-        path: this.commentSkips.next,
-        patchNum: this.patchRange.patchNum,
-        basePatchNum: this.patchRange.basePatchNum,
-      })
-    );
   }
 
   private handleNewComment() {
@@ -1198,14 +1128,14 @@
 
   private handlePrevFile() {
     if (!this.path) return;
-    if (!this.files?.sortedFileList) return;
-    this.navToFile(this.files.sortedFileList, -1);
+    if (!this.files?.sortedPaths) return;
+    this.navToFile(this.files.sortedPaths, -1);
   }
 
   private handleNextFile() {
     if (!this.path) return;
-    if (!this.files?.sortedFileList) return;
-    this.navToFile(this.files.sortedFileList, 1);
+    if (!this.files?.sortedPaths) return;
+    this.navToFile(this.files.sortedPaths, 1);
   }
 
   private handleNextChunk() {
@@ -1249,11 +1179,11 @@
 
   private navigateToUnreviewedFile(direction: string) {
     if (!this.path) return;
-    if (!this.files?.sortedFileList) return;
+    if (!this.files?.sortedPaths) return;
     if (!this.reviewedFiles) return;
     // Ensure that the currently viewed file always appears in unreviewedFiles
     // so we resolve the right "next" file.
-    const unreviewedFiles = this.files.sortedFileList.filter(
+    const unreviewedFiles = this.files.sortedPaths.filter(
       file => file === this.path || !this.reviewedFiles.has(file)
     );
 
@@ -1277,7 +1207,7 @@
       fireEvent(this, 'show-auth-required');
       return;
     }
-    this.navToChangeView(true);
+    this.getChangeModel().navigateToChange(true);
   }
 
   private handleToggleLeftPane() {
@@ -1313,10 +1243,6 @@
     this.downloadModal.close();
   }
 
-  private handleUpToChange() {
-    this.navToChangeView();
-  }
-
   private handleCommaKey() {
     if (!this.loggedIn) return;
     assertIsDefined(this.diffPreferencesDialog, 'diffPreferencesDialog');
@@ -1336,19 +1262,6 @@
   }
 
   // Private but used in tests.
-  navToChangeView(openReplyDialog = false) {
-    if (!this.changeNum || !this.patchRange?.patchNum) {
-      return;
-    }
-    this.navigateToChange(
-      this.change,
-      this.patchRange,
-      this.change && this.change.revisions,
-      openReplyDialog
-    );
-  }
-
-  // Private but used in tests.
   navToFile(
     fileList: string[],
     direction: -1 | 1,
@@ -1356,15 +1269,10 @@
   ) {
     const newPath = this.getNavLinkPath(fileList, direction);
     if (!newPath) return;
-    if (!this.change) return;
     if (!this.patchRange) return;
 
     if (newPath.up) {
-      this.navigateToChange(
-        this.change,
-        this.patchRange,
-        this.change && this.change.revisions
-      );
+      this.getChangeModel().navigateToChange();
       return;
     }
 
@@ -1375,15 +1283,7 @@
         newPath.path,
         this.patchRange
       )?.[0].line;
-    this.getNavigation().setUrl(
-      createDiffUrl({
-        change: this.change,
-        path: newPath.path,
-        patchNum: this.patchRange.patchNum,
-        basePatchNum: this.patchRange.basePatchNum,
-        lineNum,
-      })
-    );
+    this.getChangeModel().navigateToDiff({path: newPath.path, lineNum});
   }
 
   /**
@@ -1394,35 +1294,25 @@
   private computeNavLinkURL(direction?: -1 | 1) {
     if (!this.change) return;
     if (!this.path) return;
-    if (!this.files?.sortedFileList) return;
+    if (!this.files?.sortedPaths) return;
     if (!direction) return;
 
-    const newPath = this.getNavLinkPath(this.files.sortedFileList, direction);
-    if (!newPath) {
-      return;
-    }
-
-    if (newPath.up) {
-      return this.getChangePath();
-    }
-    return this.getDiffUrl(this.change, this.patchRange, newPath.path);
+    const newPath = this.getNavLinkPath(this.files.sortedPaths, direction);
+    if (!newPath) return;
+    if (newPath.up) return this.getChangeModel().changeUrl();
+    if (!newPath.path) return;
+    return this.getChangeModel().diffUrl({path: newPath.path});
   }
 
   private goToEditFile() {
-    if (!this.change) return;
-    if (!this.path) return;
-    if (!this.patchRange) return;
+    assertIsDefined(this.path, 'path');
 
     // TODO(taoalpha): add a shortcut for editing
     const cursorAddress = this.cursor?.getAddress();
-    const editUrl = createEditUrl({
-      changeNum: this.change._number,
-      repo: this.change.project,
+    this.getChangeModel().navigateToEdit({
       path: this.path,
-      patchNum: this.patchRange.patchNum,
       lineNum: cursorAddress?.number,
     });
-    this.getNavigation().setUrl(editUrl);
   }
 
   /**
@@ -1444,7 +1334,6 @@
     if (!this.path || !fileList || fileList.length === 0) {
       return null;
     }
-
     let idx = fileList.indexOf(this.path);
     if (idx === -1) {
       const file = direction > 0 ? fileList[0] : fileList[fileList.length - 1];
@@ -1462,325 +1351,74 @@
   }
 
   // Private but used in tests.
-  initLineOfInterestAndCursor(leftSide: boolean) {
-    assertIsDefined(this.diffHost, 'diffHost');
-    this.diffHost.lineOfInterest = this.getLineOfInterest(leftSide);
-    this.initCursor(leftSide);
-  }
-
-  // Private but used in tests.
-  displayDiffBaseAgainstLeftToast() {
-    if (!this.patchRange) return;
-    fireAlert(
-      this,
-      `Patchset ${this.patchRange.basePatchNum} vs ` +
-        `${this.patchRange.patchNum} selected. Press v + \u2190 to view ` +
-        `Base vs ${this.patchRange.basePatchNum}`
-    );
-  }
-
-  private displayDiffAgainstLatestToast(latestPatchNum?: PatchSetNum) {
-    if (!this.patchRange) return;
-    const leftPatchset =
-      this.patchRange.basePatchNum === PARENT
-        ? 'Base'
-        : `Patchset ${this.patchRange.basePatchNum}`;
-    fireAlert(
-      this,
-      `${leftPatchset} vs
-            ${this.patchRange.patchNum} selected\n. Press v + \u2191 to view
-            ${leftPatchset} vs Patchset ${latestPatchNum}`
-    );
-  }
-
-  private displayToasts() {
-    if (!this.patchRange) return;
-    if (this.patchRange.basePatchNum !== PARENT) {
-      this.displayDiffBaseAgainstLeftToast();
-      return;
-    }
-    const latestPatchNum = computeLatestPatchNum(this.allPatchSets);
-    if (this.patchRange.patchNum !== latestPatchNum) {
-      this.displayDiffAgainstLatestToast(latestPatchNum);
-      return;
-    }
-  }
-
-  private initCommitRange() {
-    let commit: CommitId | undefined;
-    let baseCommit: CommitId | undefined;
-    if (!this.change) return;
-    if (!this.patchRange || !this.patchRange.patchNum) return;
-    const revisions = this.change.revisions ?? {};
-    for (const [commitSha, revision] of Object.entries(revisions)) {
-      const patchNum = revision._number;
-      if (patchNum === this.patchRange.patchNum) {
-        commit = commitSha as CommitId;
-        const commitObj = revision.commit;
-        const parents = commitObj?.parents || [];
-        if (this.patchRange.basePatchNum === PARENT && parents.length) {
-          baseCommit = parents[parents.length - 1].commit;
-        }
-      } else if (patchNum === this.patchRange.basePatchNum) {
-        baseCommit = commitSha as CommitId;
-      }
-    }
-    this.commitRange = commit && baseCommit ? {commit, baseCommit} : undefined;
+  initLineOfInterestAndCursor() {
+    if (!this.diffHost) return;
+    this.diffHost.lineOfInterest = this.getLineOfInterest();
+    this.initCursor();
   }
 
   private updateUrlToDiffUrl(lineNum?: number, leftSide?: boolean) {
     if (!this.change) return;
-    if (!this.patchRange) return;
+    if (!this.patchNum) return;
     if (!this.changeNum) return;
     if (!this.path) return;
     const url = createDiffUrl({
       changeNum: this.changeNum,
       repo: this.change.project,
-      path: this.path,
-      patchNum: this.patchRange.patchNum,
-      basePatchNum: this.patchRange.basePatchNum,
-      lineNum,
-      leftSide,
+      patchNum: this.patchNum,
+      basePatchNum: this.basePatchNum,
+      diffView: {
+        path: this.path,
+        lineNum,
+        leftSide,
+      },
     });
     history.replaceState(null, '', url);
   }
 
-  // Private but used in tests.
-  initPatchRange() {
-    let leftSide = false;
-    if (!this.change) return;
-    if (this.viewState?.view !== GerritView.DIFF) return;
-    if (this.viewState?.commentId) {
-      const comment = this.changeComments?.findCommentById(
-        this.viewState.commentId
-      );
-      if (!comment) {
-        fireAlert(this, 'comment not found');
-        this.getNavigation().setUrl(createChangeUrl({change: this.change}));
-        return;
-      }
-      this.getChangeModel().updatePath(comment.path);
-
-      const latestPatchNum = computeLatestPatchNum(this.allPatchSets);
-      if (!latestPatchNum) throw new Error('Missing allPatchSets');
-      this.patchRange = getPatchRangeForCommentUrl(comment, latestPatchNum);
-      leftSide = isInBaseOfPatchRange(comment, this.patchRange);
-
-      this.focusLineNum = comment.line;
-    } else {
-      if (this.viewState.path) {
-        this.getChangeModel().updatePath(this.viewState.path);
-      }
-      if (this.viewState.patchNum) {
-        this.patchRange = {
-          patchNum: this.viewState.patchNum,
-          basePatchNum: this.viewState.basePatchNum || PARENT,
-        };
-      }
-      if (this.viewState.lineNum) {
-        this.focusLineNum = this.viewState.lineNum;
-        leftSide = !!this.viewState.leftSide;
-      }
-    }
-    assertIsDefined(this.patchRange, 'patchRange');
-    this.initLineOfInterestAndCursor(leftSide);
-
-    if (this.viewState?.commentId) {
-      // url is of type /comment/{commentId} which isn't meaningful
-      this.updateUrlToDiffUrl(this.focusLineNum, leftSide);
-    }
-
-    this.commentMap = this.getPaths();
+  async reloadDiff() {
+    if (!this.diffHost) return;
+    await this.diffHost.reload(true);
+    this.reporting.diffViewDisplayed();
+    if (this.isBlameLoaded) this.loadBlame();
   }
 
-  // Private but used in tests.
-  isFileUnchanged(diff?: DiffInfo) {
-    if (!diff || !diff.content) return false;
-    return !diff.content.some(
-      content =>
-        (content.a && !content.common) || (content.b && !content.common)
-    );
-  }
-
-  private isSameDiffLoaded(value: DiffViewState) {
-    return (
-      this.patchRange?.basePatchNum === value.basePatchNum &&
-      this.patchRange?.patchNum === value.patchNum &&
-      this.path === value.path
-    );
-  }
-
-  private async untilModelLoaded() {
-    // NOTE: Wait until this page is connected before determining whether the
-    // model is loaded.  This can happen when params are changed when setting up
-    // this view. It's unclear whether this issue is related to Polymer
-    // specifically.
-    if (!this.isConnected) {
-      await until(this.connected$, connected => connected);
-    }
-    await until(
-      this.getChangeModel().changeLoadingStatus$,
-      status => status === LoadingStatus.LOADED
-    );
-  }
-
-  // Private but used in tests.
-  viewStateChanged() {
-    if (this.viewState === undefined) return;
-    const viewState = this.viewState;
-
+  /**
+   * (Re-initialize) the diff view without actually reloading the diff. The
+   * typical user journey is that the user comes back from the change page.
+   */
+  initializePositions() {
     // The diff view is kept in the background once created. If the user
     // scrolls in the change page, the scrolling is reflected in the diff view
     // as well, which means the diff is scrolled to a random position based
     // on how much the change view was scrolled.
     // Hence, reset the scroll position here.
     document.documentElement.scrollTop = 0;
-
-    // Everything in the diff view is tied to the change. It seems better to
-    // force the re-creation of the diff view when the change number changes.
-    const changeChanged = this.changeNum !== viewState.changeNum;
-    if (this.changeNum !== undefined && changeChanged) {
-      fireEvent(this, EventType.RECREATE_DIFF_VIEW);
-      return;
-    } else if (
-      this.changeNum !== undefined &&
-      this.isSameDiffLoaded(viewState)
-    ) {
-      // changeNum has not changed, so check if there are changes in patchRange
-      // path. If no changes then we can simply render the view as is.
-      this.reporting.reportInteraction('diff-view-re-rendered');
-      // Make sure to re-initialize the cursor because this is typically
-      // done on the 'render' event which doesn't fire in this path as
-      // rerendering is avoided.
-      this.reInitCursor();
-      this.diffHost?.initLayers();
-      return;
-    }
-
-    this.files = {sortedFileList: [], changeFilesByPath: {}};
-    if (this.isConnected) {
-      this.getChangeModel().updatePath(undefined);
-    }
-    this.patchRange = undefined;
-    this.commitRange = undefined;
-    this.focusLineNum = undefined;
-
-    if (viewState.changeNum && viewState.repo) {
-      this.restApiService.setInProjectLookup(
-        viewState.changeNum,
-        viewState.repo
-      );
-    }
-
-    this.changeNum = viewState.changeNum;
+    this.reInitCursor();
+    this.diffHost?.initLayers();
     this.classList.remove('hideComments');
-
-    // When navigating away from the page, there is a possibility that the
-    // patch number is no longer a part of the URL (say when navigating to
-    // the top-level change info view) and therefore undefined in `params`.
-    // If route is of type /comment/<commentId>/ then no patchNum is present
-    if (!viewState.patchNum && !viewState.commentLink) {
-      this.reporting.error(
-        'GrDiffView',
-        new Error(`Invalid diff view URL, no patchNum found: ${this.viewState}`)
-      );
-      return;
-    }
-
-    const promises: Promise<unknown>[] = [];
-    if (!this.change) {
-      promises.push(this.untilModelLoaded());
-    }
-    promises.push(this.waitUntilCommentsLoaded());
-
-    if (this.diffHost) {
-      this.diffHost.cancel();
-      this.diffHost.clearDiffContent();
-    }
-    this.loading = true;
-    return Promise.all(promises)
-      .then(() => {
-        this.loading = false;
-        this.initPatchRange();
-        this.initCommitRange();
-        return this.updateComplete.then(() => this.diffHost!.reload(true));
-      })
-      .then(() => {
-        this.reporting.diffViewDisplayed();
-      })
-      .then(() => {
-        const fileUnchanged = this.isFileUnchanged(this.diff);
-        if (fileUnchanged && viewState.commentLink) {
-          assertIsDefined(this.change, 'change');
-          assertIsDefined(this.path, 'path');
-          assertIsDefined(this.patchRange, 'patchRange');
-
-          if (this.patchRange.basePatchNum === PARENT) {
-            // file is unchanged between Base vs X
-            // hence should not show diff between Base vs Base
-            return;
-          }
-
-          fireAlert(
-            this,
-            `File is unchanged between Patchset
-                  ${this.patchRange.basePatchNum} and
-                  ${this.patchRange.patchNum}. Showing diff of Base vs
-                  ${this.patchRange.basePatchNum}`
-          );
-          this.getNavigation().setUrl(
-            createDiffUrl({
-              change: this.change,
-              path: this.path,
-              patchNum: this.patchRange.basePatchNum as RevisionPatchSetNum,
-              basePatchNum: PARENT,
-              lineNum: this.focusLineNum,
-            })
-          );
-          return;
-        }
-        if (viewState.commentLink) {
-          this.displayToasts();
-        }
-        // If the blame was loaded for a previous file and user navigates to
-        // another file, then we load the blame for this file too
-        if (this.isBlameLoaded) this.loadBlame();
-      });
-  }
-
-  private async waitUntilCommentsLoaded() {
-    await until(this.connected$, c => c);
-    await until(this.getCommentsModel().commentsLoading$, isFalse);
   }
 
   /**
    * If the params specify a diff address then configure the diff cursor.
    * Private but used in tests.
    */
-  initCursor(leftSide: boolean) {
-    if (this.focusLineNum === undefined) {
-      return;
-    }
+  initCursor() {
+    if (!this.focusLineNum) return;
     if (!this.cursor) return;
-    if (leftSide) {
-      this.cursor.side = Side.LEFT;
-    } else {
-      this.cursor.side = Side.RIGHT;
-    }
+    this.cursor.side = this.leftSide ? Side.LEFT : Side.RIGHT;
     this.cursor.initialLineNumber = this.focusLineNum;
   }
 
   // Private but used in tests.
-  getLineOfInterest(leftSide: boolean): DisplayLine | undefined {
+  getLineOfInterest(): DisplayLine | undefined {
     // If there is a line number specified, pass it along to the diff so that
     // it will not get collapsed.
-    if (!this.focusLineNum) {
-      return undefined;
-    }
+    if (!this.focusLineNum) return undefined;
 
     return {
       lineNum: this.focusLineNum,
-      side: leftSide ? Side.LEFT : Side.RIGHT,
+      side: this.leftSide ? Side.LEFT : Side.RIGHT,
     };
   }
 
@@ -1790,83 +1428,6 @@
     }
   }
 
-  private getDiffUrl(
-    change?: ChangeInfo | ParsedChangeInfo,
-    patchRange?: PatchRange,
-    path?: string
-  ) {
-    if (!change || !patchRange || !path) return '';
-    return createDiffUrl({
-      changeNum: change._number,
-      repo: change.project,
-      path,
-      patchNum: patchRange.patchNum,
-      basePatchNum: patchRange.basePatchNum,
-    });
-  }
-
-  /**
-   * When the latest patch of the change is selected (and there is no base
-   * patch) then the patch range need not appear in the URL. Return a patch
-   * range object with undefined values when a range is not needed.
-   */
-  private getChangeUrlRange(
-    patchRange?: PatchRange,
-    revisions?: {[revisionId: string]: RevisionInfo | EditRevisionInfo}
-  ) {
-    let patchNum = undefined;
-    let basePatchNum = undefined;
-    let latestPatchNum = -1;
-    for (const rev of Object.values(revisions || {})) {
-      if (typeof rev._number === 'number') {
-        latestPatchNum = Math.max(latestPatchNum, rev._number);
-      }
-    }
-    if (!patchRange) return {patchNum, basePatchNum};
-    if (
-      patchRange.basePatchNum !== PARENT ||
-      patchRange.patchNum !== latestPatchNum
-    ) {
-      patchNum = patchRange.patchNum;
-      basePatchNum = patchRange.basePatchNum;
-    }
-    return {patchNum, basePatchNum};
-  }
-
-  private getChangePath() {
-    if (!this.change) return '';
-    if (!this.patchRange) return '';
-
-    const range = this.getChangeUrlRange(
-      this.patchRange,
-      this.change.revisions
-    );
-    return createChangeUrl({
-      change: this.change,
-      patchNum: range.patchNum,
-      basePatchNum: range.basePatchNum,
-    });
-  }
-
-  // Private but used in tests.
-  navigateToChange(
-    change?: ChangeInfo | ParsedChangeInfo,
-    patchRange?: PatchRange,
-    revisions?: {[revisionId: string]: RevisionInfo | EditRevisionInfo},
-    openReplyDialog?: boolean
-  ) {
-    if (!change) return;
-    const range = this.getChangeUrlRange(patchRange, revisions);
-    this.getNavigation().setUrl(
-      createChangeUrl({
-        change,
-        patchNum: range.patchNum,
-        basePatchNum: range.basePatchNum,
-        openReplyDialog: !!openReplyDialog,
-      })
-    );
-  }
-
   // Private but used in tests
   formatFilesForDropdown(): DropdownItem[] {
     if (!this.files) return [];
@@ -1874,7 +1435,8 @@
     if (!this.changeComments) return [];
 
     const dropdownContent: DropdownItem[] = [];
-    for (const path of this.files.sortedFileList) {
+    for (const path of this.files.sortedPaths) {
+      const file = this.files.changeFilesByPath[path];
       dropdownContent.push({
         text: computeDisplayPath(path),
         mobileText: computeTruncatedPath(path),
@@ -1882,10 +1444,10 @@
         bottomText: this.changeComments.computeCommentsString(
           this.patchRange,
           path,
-          this.files.changeFilesByPath[path],
+          file,
           /* includeUnmodified= */ true
         ),
-        file: {...this.files.changeFilesByPath[path], __path: path},
+        file,
       });
     }
     return dropdownContent;
@@ -1893,45 +1455,24 @@
 
   // Private but used in tests.
   handleFileChange(e: CustomEvent) {
-    if (!this.change) return;
-    if (!this.patchRange) return;
-
-    // This is when it gets set initially.
     const path = e.detail.value;
-    if (path === this.path) {
-      return;
-    }
-
-    this.getNavigation().setUrl(
-      createDiffUrl({
-        change: this.change,
-        path,
-        patchNum: this.patchRange.patchNum,
-        basePatchNum: this.patchRange.basePatchNum,
-      })
-    );
+    if (path === this.path) return;
+    this.getChangeModel().navigateToDiff(path);
   }
 
   // Private but used in tests.
   handlePatchChange(e: CustomEvent) {
-    if (!this.change) return;
     if (!this.path) return;
-    if (!this.patchRange) return;
+    if (!this.patchNum) return;
 
     const {basePatchNum, patchNum} = e.detail;
-    if (
-      basePatchNum === this.patchRange.basePatchNum &&
-      patchNum === this.patchRange.patchNum
-    ) {
+    if (basePatchNum === this.basePatchNum && patchNum === this.patchNum) {
       return;
     }
-    this.getNavigation().setUrl(
-      createDiffUrl({
-        change: this.change,
-        path: this.path,
-        patchNum,
-        basePatchNum,
-      })
+    this.getChangeModel().navigateToDiff(
+      {path: this.path},
+      patchNum,
+      basePatchNum
     );
   }
 
@@ -1956,7 +1497,7 @@
   computeDownloadDropdownLinks() {
     if (!this.change?.project) return [];
     if (!this.changeNum) return [];
-    if (!this.patchRange?.patchNum) return [];
+    if (!this.patchRange) return [];
     if (!this.path) return [];
 
     const links = [
@@ -2004,6 +1545,7 @@
     return links;
   }
 
+  // TODO: Move to view-model or router.
   // Private but used in tests.
   computeDownloadFileLink(
     repo: RepoName,
@@ -2032,6 +1574,7 @@
     return url;
   }
 
+  // TODO: Move to view-model or router.
   // Private but used in tests.
   computeDownloadPatchLink(
     repo: RepoName,
@@ -2045,49 +1588,19 @@
   }
 
   // Private but used in tests.
-  getPaths(): CommentMap {
-    if (!this.changeComments) return {};
-    return this.changeComments.getPaths(this.patchRange);
-  }
+  findFileWithComment(direction: -1 | 1): string | undefined {
+    const fileList = this.files?.sortedPaths;
+    const commentMap: CommentMap =
+      this.changeComments?.getPaths(this.patchRange) ?? {};
+    if (!fileList || fileList.length === 0) return undefined;
+    if (!this.path) return undefined;
 
-  // Private but used in tests.
-  computeCommentSkips(
-    commentMap?: CommentMap,
-    fileList?: string[],
-    path?: string
-  ): CommentSkips | undefined {
-    if (!commentMap) return undefined;
-    if (!fileList) return undefined;
-    if (!path) return undefined;
-
-    const skips: CommentSkips = {previous: null, next: null};
-    if (!fileList.length) {
-      return skips;
+    const pathIndex = fileList.indexOf(this.path);
+    const stopIndex = direction === 1 ? fileList.length : -1;
+    for (let i = pathIndex + direction; i !== stopIndex; i += direction) {
+      if (commentMap[fileList[i]]) return fileList[i];
     }
-    const pathIndex = fileList.indexOf(path);
-
-    // Scan backward for the previous file.
-    for (let i = pathIndex - 1; i >= 0; i--) {
-      if (commentMap[fileList[i]]) {
-        skips.previous = fileList[i];
-        break;
-      }
-    }
-
-    // Scan forward for the next file.
-    for (let i = pathIndex + 1; i < fileList.length; i++) {
-      if (commentMap[fileList[i]]) {
-        skips.next = fileList[i];
-        break;
-      }
-    }
-
-    return skips;
-  }
-
-  // Private but used in tests.
-  computeEditMode() {
-    return this.patchRange?.patchNum === EDIT;
+    return undefined;
   }
 
   // Private but used in tests.
@@ -2130,111 +1643,89 @@
 
   // Private but used in tests.
   handleDiffAgainstBase() {
-    if (!this.change) return;
-    if (!this.path) return;
-    if (!this.patchRange) return;
+    if (!this.isActiveChildView) return;
+    assertIsDefined(this.path, 'path');
+    assertIsDefined(this.patchNum, 'patchNum');
 
-    if (this.patchRange.basePatchNum === PARENT) {
+    if (this.basePatchNum === PARENT) {
       fireAlert(this, 'Base is already selected.');
       return;
     }
-    this.getNavigation().setUrl(
-      createDiffUrl({
-        change: this.change,
-        path: this.path,
-        patchNum: this.patchRange.patchNum,
-      })
+    this.getChangeModel().navigateToDiff(
+      {path: this.path},
+      this.patchNum,
+      PARENT
     );
   }
 
   // Private but used in tests.
   handleDiffBaseAgainstLeft() {
-    if (!this.change) return;
-    if (!this.path) return;
-    if (!this.patchRange) return;
+    if (!this.isActiveChildView) return;
+    assertIsDefined(this.path, 'path');
+    assertIsDefined(this.patchNum, 'patchNum');
 
-    if (this.patchRange.basePatchNum === PARENT) {
+    if (this.basePatchNum === PARENT) {
       fireAlert(this, 'Left is already base.');
       return;
     }
-    const lineNum =
-      this.viewState?.view === GerritView.DIFF && this.viewState?.commentLink
-        ? this.focusLineNum
-        : undefined;
-    this.getNavigation().setUrl(
-      createDiffUrl({
-        change: this.change,
-        path: this.path,
-        patchNum: this.patchRange.basePatchNum as RevisionPatchSetNum,
-        basePatchNum: PARENT,
-        lineNum,
-      })
+    this.getChangeModel().navigateToDiff(
+      {path: this.path},
+      this.basePatchNum as RevisionPatchSetNum,
+      PARENT
     );
   }
 
   // Private but used in tests.
   handleDiffAgainstLatest() {
-    if (!this.change) return;
-    if (!this.path) return;
-    if (!this.patchRange) return;
+    if (!this.isActiveChildView) return;
+    assertIsDefined(this.path, 'path');
+    assertIsDefined(this.patchNum, 'patchNum');
 
-    const latestPatchNum = computeLatestPatchNum(this.allPatchSets);
-    if (this.patchRange.patchNum === latestPatchNum) {
+    if (this.patchNum === this.latestPatchNum) {
       fireAlert(this, 'Latest is already selected.');
       return;
     }
 
-    this.getNavigation().setUrl(
-      createDiffUrl({
-        change: this.change,
-        path: this.path,
-        patchNum: latestPatchNum,
-        basePatchNum: this.patchRange.basePatchNum,
-      })
+    this.getChangeModel().navigateToDiff(
+      {path: this.path},
+      this.latestPatchNum,
+      this.basePatchNum
     );
   }
 
   // Private but used in tests.
   handleDiffRightAgainstLatest() {
-    if (!this.change) return;
-    if (!this.path) return;
-    if (!this.patchRange) return;
+    if (!this.isActiveChildView) return;
+    assertIsDefined(this.path, 'path');
+    assertIsDefined(this.patchNum, 'patchNum');
 
-    const latestPatchNum = computeLatestPatchNum(this.allPatchSets);
-    if (this.patchRange.patchNum === latestPatchNum) {
+    if (this.patchNum === this.latestPatchNum) {
       fireAlert(this, 'Right is already latest.');
       return;
     }
-    this.getNavigation().setUrl(
-      createDiffUrl({
-        change: this.change,
-        path: this.path,
-        patchNum: latestPatchNum,
-        basePatchNum: this.patchRange.patchNum as BasePatchSetNum,
-      })
+
+    this.getChangeModel().navigateToDiff(
+      {path: this.path},
+      this.latestPatchNum,
+      this.patchNum as BasePatchSetNum
     );
   }
 
   // Private but used in tests.
   handleDiffBaseAgainstLatest() {
-    if (!this.change) return;
-    if (!this.path) return;
-    if (!this.patchRange) return;
+    if (!this.isActiveChildView) return;
+    assertIsDefined(this.path, 'path');
+    assertIsDefined(this.patchNum, 'patchNum');
 
-    const latestPatchNum = computeLatestPatchNum(this.allPatchSets);
-    if (
-      this.patchRange.patchNum === latestPatchNum &&
-      this.patchRange.basePatchNum === PARENT
-    ) {
+    if (this.patchNum === this.latestPatchNum && this.basePatchNum === PARENT) {
       fireAlert(this, 'Already diffing base against latest.');
       return;
     }
-    this.getNavigation().setUrl(
-      createDiffUrl({
-        change: this.change,
-        path: this.path,
-        patchNum: latestPatchNum,
-      })
+
+    this.getChangeModel().navigateToDiff(
+      {path: this.path},
+      this.latestPatchNum,
+      PARENT
     );
   }
 
@@ -2265,13 +1756,13 @@
 
   private navigateToNextFileWithCommentThread() {
     if (!this.path) return;
-    if (!this.files?.sortedFileList) return;
-    if (!this.patchRange) return;
+    if (!this.files?.sortedPaths) return;
+    const range = this.patchRange;
+    if (!range) return;
     if (!this.change) return;
     const hasComment = (path: string) =>
-      this.changeComments?.getCommentsForPath(path, this.patchRange!)?.length ??
-      0 > 0;
-    const filesWithComments = this.files.sortedFileList.filter(
+      this.changeComments?.getCommentsForPath(path, range)?.length ?? 0 > 0;
+    const filesWithComments = this.files.sortedPaths.filter(
       file => file === this.path || hasComment(file)
     );
     this.navToFile(filesWithComments, 1, true);
diff --git a/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view_test.ts b/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view_test.ts
index 6a565eb..1999a82 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view_test.ts
+++ b/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view_test.ts
@@ -5,7 +5,6 @@
  */
 import '../../../test/common-test-setup';
 import './gr-diff-view';
-import {navigationToken} from '../../core/gr-navigation/gr-navigation';
 import {
   ChangeStatus,
   DiffViewMode,
@@ -18,38 +17,29 @@
   query,
   queryAll,
   queryAndAssert,
-  stubReporting,
   stubRestApi,
   waitEventLoop,
   waitUntil,
 } from '../../../test/test-utils';
 import {ChangeComments} from '../gr-comment-api/gr-comment-api';
 import {
-  GerritView,
-  routerModelToken,
-} from '../../../services/router/router-model';
-import {
   createRevisions,
   createComment as createCommentGeneric,
-  TEST_NUMERIC_CHANGE_ID,
   createDiff,
-  createPatchRange,
   createServerInfo,
   createConfig,
   createParsedChange,
   createRevision,
-  createCommit,
   createFileInfo,
+  createDiffViewState,
+  TEST_NUMERIC_CHANGE_ID,
 } from '../../../test/test-data-generators';
 import {
   BasePatchSetNum,
   CommentInfo,
-  CommitId,
   EDIT,
-  FileInfo,
   NumericChangeId,
   PARENT,
-  PatchRange,
   PatchSetNum,
   PatchSetNumber,
   PathToCommentsInfoMap,
@@ -58,17 +48,15 @@
   UrlEncodedCommentId,
 } from '../../../types/common';
 import {CursorMoveResult} from '../../../api/core';
-import {DiffInfo, Side} from '../../../api/diff';
+import {Side} from '../../../api/diff';
 import {Files, GrDiffView} from './gr-diff-view';
 import {DropdownItem} from '../../shared/gr-dropdown-list/gr-dropdown-list';
-import {SinonFakeTimers, SinonStub, SinonSpy} from 'sinon';
+import {SinonFakeTimers, SinonStub} from 'sinon';
 import {
   changeModelToken,
   ChangeModel,
   LoadingStatus,
 } from '../../../models/change/change-model';
-import {CommentMap} from '../../../utils/comment-util';
-import {ParsedChangeInfo} from '../../../types/types';
 import {assertIsDefined} from '../../../utils/common-util';
 import {GrDiffModeSelector} from '../../../embed/diff/gr-diff-mode-selector/gr-diff-mode-selector';
 import {fixture, html, assert} from '@open-wc/testing';
@@ -85,6 +73,11 @@
   BrowserModel,
   browserModelToken,
 } from '../../../models/browser/browser-model';
+import {
+  ChangeViewModel,
+  changeViewModelToken,
+} from '../../../models/views/change';
+import {FileNameToNormalizedFileInfoMap} from '../../../models/change/files-model';
 
 function createComment(
   id: string,
@@ -107,25 +100,27 @@
     let clock: SinonFakeTimers;
     let diffCommentsStub;
     let getDiffRestApiStub: SinonStub;
-    let setUrlStub: SinonStub;
+    let navToChangeStub: SinonStub;
+    let navToDiffStub: SinonStub;
+    let navToEditStub: SinonStub;
     let changeModel: ChangeModel;
+    let viewModel: ChangeViewModel;
     let commentsModel: CommentsModel;
     let browserModel: BrowserModel;
     let userModel: UserModel;
 
     function getFilesFromFileList(fileList: string[]): Files {
       const changeFilesByPath = fileList.reduce((files, path) => {
-        files[path] = createFileInfo();
+        files[path] = createFileInfo(path);
         return files;
-      }, {} as {[path: string]: FileInfo});
+      }, {} as FileNameToNormalizedFileInfoMap);
       return {
-        sortedFileList: fileList,
+        sortedPaths: fileList,
         changeFilesByPath,
       };
     }
 
     setup(async () => {
-      setUrlStub = sinon.stub(testResolver(navigationToken), 'setUrl');
       stubRestApi('getConfig').returns(Promise.resolve(createServerInfo()));
       stubRestApi('getLoggedIn').returns(Promise.resolve(false));
       stubRestApi('getProjectConfig').returns(Promise.resolve(createConfig()));
@@ -144,14 +139,17 @@
       stubRestApi('getPortedComments').returns(Promise.resolve({}));
 
       element = await fixture(html`<gr-diff-view></gr-diff-view>`);
-      element.changeNum = 42 as NumericChangeId;
+      viewModel = testResolver(changeViewModelToken);
+      viewModel.setState(createDiffViewState());
+      await waitUntil(() => element.changeNum === TEST_NUMERIC_CHANGE_ID);
       element.path = 'some/path.txt';
       element.change = createParsedChange();
       element.diff = {...createDiff(), content: []};
       getDiffRestApiStub = stubRestApi('getDiff');
       // Delayed in case a test updates element.diff.
       getDiffRestApiStub.callsFake(() => Promise.resolve(element.diff));
-      element.patchRange = createPatchRange();
+      element.patchNum = 1 as RevisionPatchSetNum;
+      element.basePatchNum = PARENT;
       element.changeComments = new ChangeComments({
         '/COMMIT_MSG': [
           createComment('c1', 10, 2, '/COMMIT_MSG'),
@@ -163,6 +161,9 @@
       changeModel = testResolver(changeModelToken);
       browserModel = testResolver(browserModelToken);
       userModel = testResolver(userModelToken);
+      navToChangeStub = sinon.stub(changeModel, 'navigateToChange');
+      navToDiffStub = sinon.stub(changeModel, 'navigateToDiff');
+      navToEditStub = sinon.stub(changeModel, 'navigateToEdit');
 
       commentsModel.setState({
         comments: {},
@@ -179,279 +180,6 @@
       sinon.restore();
     });
 
-    test('viewState change triggers diffViewDisplayed()', () => {
-      const diffViewDisplayedStub = stubReporting('diffViewDisplayed');
-      assertIsDefined(element.diffHost);
-      sinon.stub(element.diffHost, 'reload').returns(Promise.resolve());
-      sinon.stub(element, 'initPatchRange');
-      sinon.stub(element, 'fetchFiles');
-      const viewStateChangedSpy = sinon.spy(element, 'viewStateChanged');
-      element.viewState = {
-        view: GerritView.DIFF,
-        changeNum: 42 as NumericChangeId,
-        patchNum: 2 as RevisionPatchSetNum,
-        basePatchNum: 1 as BasePatchSetNum,
-        path: '/COMMIT_MSG',
-      };
-      element.path = '/COMMIT_MSG';
-      element.patchRange = createPatchRange();
-      return viewStateChangedSpy.returnValues[0]?.then(() => {
-        assert.isTrue(diffViewDisplayedStub.calledOnce);
-      });
-    });
-
-    suite('comment route', () => {
-      let initLineOfInterestAndCursorStub: SinonStub;
-      let replaceStateStub: SinonStub;
-      let viewStateChangedSpy: SinonSpy;
-      setup(() => {
-        initLineOfInterestAndCursorStub = sinon.stub(
-          element,
-          'initLineOfInterestAndCursor'
-        );
-        replaceStateStub = sinon.stub(history, 'replaceState');
-        sinon.stub(element, 'fetchFiles');
-        stubReporting('diffViewDisplayed');
-        assertIsDefined(element.diffHost);
-        sinon.stub(element.diffHost, 'reload').returns(Promise.resolve());
-        viewStateChangedSpy = sinon.spy(element, 'viewStateChanged');
-        changeModel.setState({
-          change: {
-            ...createParsedChange(),
-            revisions: createRevisions(11),
-          },
-          loadingStatus: LoadingStatus.LOADED,
-        });
-      });
-
-      test('comment url resolves to comment.patch_set vs latest', () => {
-        commentsModel.setState({
-          comments: {
-            '/COMMIT_MSG': [
-              createComment('c1', 10, 2, '/COMMIT_MSG'),
-              createComment('c3', 10, PARENT, '/COMMIT_MSG'),
-            ],
-          },
-          robotComments: {},
-          drafts: {},
-          portedComments: {},
-          portedDrafts: {},
-          discardedDrafts: [],
-        });
-        element.viewState = {
-          view: GerritView.DIFF,
-          changeNum: 42 as NumericChangeId,
-          commentLink: true,
-          commentId: 'c1' as UrlEncodedCommentId,
-          path: 'abcd',
-          patchNum: 1 as RevisionPatchSetNum,
-        };
-        element.change = {
-          ...createParsedChange(),
-          revisions: createRevisions(11),
-        };
-        return viewStateChangedSpy.returnValues[0].then(() => {
-          assert.isTrue(
-            initLineOfInterestAndCursorStub.calledWithExactly(true)
-          );
-          assert.equal(element.focusLineNum, 10);
-          assert.equal(element.patchRange?.patchNum, 11 as RevisionPatchSetNum);
-          assert.equal(element.patchRange?.basePatchNum, 2 as BasePatchSetNum);
-          assert.isTrue(replaceStateStub.called);
-        });
-      });
-    });
-
-    test('viewState change causes blame to load if it was set to true', () => {
-      // Blame loads for subsequent files if it was loaded for one file
-      element.isBlameLoaded = true;
-      stubReporting('diffViewDisplayed');
-      const loadBlameStub = sinon.stub(element, 'loadBlame');
-      assertIsDefined(element.diffHost);
-      sinon.stub(element.diffHost, 'reload').returns(Promise.resolve());
-      const viewStateChangedSpy = sinon.spy(element, 'viewStateChanged');
-      sinon.stub(element, 'initPatchRange');
-      sinon.stub(element, 'fetchFiles');
-      element.viewState = {
-        view: GerritView.DIFF,
-        changeNum: 42 as NumericChangeId,
-        patchNum: 2 as RevisionPatchSetNum,
-        basePatchNum: 1 as BasePatchSetNum,
-        path: '/COMMIT_MSG',
-      };
-      element.path = '/COMMIT_MSG';
-      element.patchRange = createPatchRange();
-      return viewStateChangedSpy.returnValues[0]!.then(() => {
-        assert.isTrue(element.isBlameLoaded);
-        assert.isTrue(loadBlameStub.calledOnce);
-      });
-    });
-
-    test('unchanged diff X vs latest from comment links navigates to base vs X', async () => {
-      commentsModel.setState({
-        comments: {
-          '/COMMIT_MSG': [
-            createComment('c1', 10, 2, '/COMMIT_MSG'),
-            createComment('c3', 10, PARENT, '/COMMIT_MSG'),
-          ],
-        },
-        robotComments: {},
-        drafts: {},
-        portedComments: {},
-        portedDrafts: {},
-        discardedDrafts: [],
-      });
-      stubReporting('diffViewDisplayed');
-      sinon.stub(element, 'loadBlame');
-      assertIsDefined(element.diffHost);
-      sinon.stub(element.diffHost, 'reload').returns(Promise.resolve());
-      sinon.stub(element, 'isFileUnchanged').returns(true);
-      const viewStateChangedSpy = sinon.spy(element, 'viewStateChanged');
-      changeModel.setState({
-        change: {
-          ...createParsedChange(),
-          revisions: createRevisions(11),
-        },
-        loadingStatus: LoadingStatus.LOADED,
-      });
-      element.viewState = {
-        view: GerritView.DIFF,
-        changeNum: 42 as NumericChangeId,
-        path: '/COMMIT_MSG',
-        commentLink: true,
-        commentId: 'c1' as UrlEncodedCommentId,
-      };
-      element.change = {
-        ...createParsedChange(),
-        revisions: createRevisions(11),
-      };
-      await viewStateChangedSpy.returnValues[0];
-      assert.isTrue(setUrlStub.calledOnce);
-      assert.equal(
-        setUrlStub.lastCall.firstArg,
-        '/c/test-project/+/42/2//COMMIT_MSG#10'
-      );
-    });
-
-    test('unchanged diff Base vs latest from comment does not navigate', async () => {
-      commentsModel.setState({
-        comments: {
-          '/COMMIT_MSG': [
-            createComment('c1', 10, 2, '/COMMIT_MSG'),
-            createComment('c3', 10, PARENT, '/COMMIT_MSG'),
-          ],
-        },
-        robotComments: {},
-        drafts: {},
-        portedComments: {},
-        portedDrafts: {},
-        discardedDrafts: [],
-      });
-      stubReporting('diffViewDisplayed');
-      sinon.stub(element, 'loadBlame');
-      assertIsDefined(element.diffHost);
-      sinon.stub(element.diffHost, 'reload').returns(Promise.resolve());
-      sinon.stub(element, 'isFileUnchanged').returns(true);
-      const viewStateChangedSpy = sinon.spy(element, 'viewStateChanged');
-      changeModel.setState({
-        change: {
-          ...createParsedChange(),
-          revisions: createRevisions(11),
-        },
-        loadingStatus: LoadingStatus.LOADED,
-      });
-      element.viewState = {
-        view: GerritView.DIFF,
-        changeNum: 42 as NumericChangeId,
-        path: '/COMMIT_MSG',
-        commentLink: true,
-        commentId: 'c3' as UrlEncodedCommentId,
-      };
-      element.change = {
-        ...createParsedChange(),
-        revisions: createRevisions(11),
-      };
-      await viewStateChangedSpy.returnValues[0];
-      assert.isFalse(setUrlStub.calledOnce);
-    });
-
-    test('isFileUnchanged', () => {
-      let diff: DiffInfo = {
-        ...createDiff(),
-        content: [
-          {a: ['abcd'], ab: ['ef']},
-          {b: ['ancd'], a: ['xx']},
-        ],
-      };
-      assert.equal(element.isFileUnchanged(diff), false);
-      diff = {
-        ...createDiff(),
-        content: [{ab: ['abcd']}, {ab: ['ancd']}],
-      };
-      assert.equal(element.isFileUnchanged(diff), true);
-      diff = {
-        ...createDiff(),
-        content: [
-          {a: ['abcd'], ab: ['ef'], common: true},
-          {b: ['ancd'], ab: ['xx']},
-        ],
-      };
-      assert.equal(element.isFileUnchanged(diff), false);
-      diff = {
-        ...createDiff(),
-        content: [
-          {a: ['abcd'], ab: ['ef'], common: true},
-          {b: ['ancd'], ab: ['xx'], common: true},
-        ],
-      };
-      assert.equal(element.isFileUnchanged(diff), true);
-    });
-
-    test('diff toast to go to latest is shown and not base', async () => {
-      commentsModel.setState({
-        comments: {
-          '/COMMIT_MSG': [
-            createComment('c1', 10, 2, '/COMMIT_MSG'),
-            createComment('c3', 10, PARENT, '/COMMIT_MSG'),
-          ],
-        },
-        robotComments: {},
-        drafts: {},
-        portedComments: {},
-        portedDrafts: {},
-        discardedDrafts: [],
-      });
-
-      stubReporting('diffViewDisplayed');
-      sinon.stub(element, 'loadBlame');
-      assertIsDefined(element.diffHost);
-      sinon.stub(element.diffHost, 'reload').returns(Promise.resolve());
-      const viewStateChangedSpy = sinon.spy(element, 'viewStateChanged');
-      element.change = undefined;
-      changeModel.setState({
-        change: {
-          ...createParsedChange(),
-          revisions: createRevisions(11),
-        },
-        loadingStatus: LoadingStatus.LOADED,
-      });
-      element.patchRange = {
-        patchNum: 2 as RevisionPatchSetNum,
-        basePatchNum: 1 as BasePatchSetNum,
-      };
-      sinon.stub(element, 'isFileUnchanged').returns(false);
-      const toastStub = sinon.stub(element, 'displayDiffBaseAgainstLeftToast');
-      element.viewState = {
-        view: GerritView.DIFF,
-        changeNum: 42 as NumericChangeId,
-        repo: 'p' as RepoName,
-        commentId: 'c1' as UrlEncodedCommentId,
-        commentLink: true,
-      };
-      await viewStateChangedSpy.returnValues[0];
-      assert.isTrue(toastStub.called);
-    });
-
     test('toggle left diff with a hotkey', () => {
       assertIsDefined(element.diffHost);
       const toggleLeftDiffStub = sinon.stub(element.diffHost, 'toggleLeftDiff');
@@ -460,20 +188,17 @@
     });
 
     test('renders', async () => {
-      clock = sinon.useFakeTimers();
-      element.changeNum = 42 as NumericChangeId;
       browserModel.setScreenWidth(0);
-      element.patchRange = {
-        basePatchNum: PARENT,
-        patchNum: 10 as RevisionPatchSetNum,
-      };
-      element.change = {
+      element.patchNum = 10 as RevisionPatchSetNum;
+      element.basePatchNum = PARENT;
+      const change = {
         ...createParsedChange(),
         _number: 42 as NumericChangeId,
         revisions: {
           a: createRevision(10),
         },
       };
+      changeModel.updateStateChange(change);
       element.files = getFilesFromFileList([
         'chell.go',
         'glados.txt',
@@ -625,9 +350,8 @@
               </a>
             </div>
           </div>
-          <div class="loading">Loading...</div>
           <h2 class="assistive-tech-only">Diff view</h2>
-          <gr-diff-host hidden="" id="diffHost"> </gr-diff-host>
+          <gr-diff-host id="diffHost"> </gr-diff-host>
           <gr-apply-fix-dialog id="applyFixDialog"> </gr-apply-fix-dialog>
           <gr-diff-preferences-dialog id="diffPreferencesDialog">
           </gr-diff-preferences-dialog>
@@ -643,10 +367,8 @@
       clock = sinon.useFakeTimers();
       element.changeNum = 42 as NumericChangeId;
       browserModel.setScreenWidth(0);
-      element.patchRange = {
-        basePatchNum: PARENT,
-        patchNum: 10 as RevisionPatchSetNum,
-      };
+      element.patchNum = 10 as RevisionPatchSetNum;
+      element.basePatchNum = PARENT;
       element.change = {
         ...createParsedChange(),
         _number: 42 as NumericChangeId,
@@ -662,51 +384,42 @@
       element.path = 'glados.txt';
       element.loggedIn = true;
       await element.updateComplete;
-      setUrlStub.reset();
+      navToChangeStub.reset();
 
       pressKey(element, 'u');
-      assert.equal(setUrlStub.callCount, 1);
-      assert.equal(setUrlStub.lastCall.firstArg, '/c/test-project/+/42');
+      assert.isTrue(navToChangeStub.calledOnce);
       await element.updateComplete;
 
       pressKey(element, ']');
-      assert.equal(setUrlStub.callCount, 2);
-      assert.equal(
-        setUrlStub.lastCall.firstArg,
-        '/c/test-project/+/42/10/wheatley.md'
-      );
+      assert.equal(navToDiffStub.callCount, 1);
+      assert.deepEqual(navToDiffStub.lastCall.args, [
+        {path: 'wheatley.md', lineNum: undefined},
+      ]);
+
       element.path = 'wheatley.md';
       await element.updateComplete;
 
-      assert.isTrue(element.loading);
-
       pressKey(element, '[');
-      assert.equal(setUrlStub.callCount, 3);
-      assert.equal(
-        setUrlStub.lastCall.firstArg,
-        '/c/test-project/+/42/10/glados.txt'
-      );
+      assert.equal(navToDiffStub.callCount, 2);
+      assert.deepEqual(navToDiffStub.lastCall.args, [
+        {path: 'glados.txt', lineNum: undefined},
+      ]);
+
       element.path = 'glados.txt';
       await element.updateComplete;
 
-      assert.isTrue(element.loading);
-
       pressKey(element, '[');
-      assert.equal(setUrlStub.callCount, 4);
-      assert.equal(
-        setUrlStub.lastCall.firstArg,
-        '/c/test-project/+/42/10/chell.go'
-      );
+      assert.equal(navToDiffStub.callCount, 3);
+      assert.deepEqual(navToDiffStub.lastCall.args, [
+        {path: 'chell.go', lineNum: undefined},
+      ]);
+
       element.path = 'chell.go';
       await element.updateComplete;
 
-      assert.isTrue(element.loading);
-
       pressKey(element, '[');
-      assert.equal(setUrlStub.callCount, 5);
-      assert.equal(setUrlStub.lastCall.firstArg, '/c/test-project/+/42');
+      assert.equal(navToChangeStub.callCount, 2);
       await element.updateComplete;
-      assert.isTrue(element.loading);
 
       assertIsDefined(element.diffPreferencesDialog);
       const showPrefsStub = sinon
@@ -756,12 +469,8 @@
       );
       assert.isFalse(element.diffHost.diffElement.displayLine);
 
-      // Note that stubbing setReviewed means that the value of the
-      // `element.reviewed` checkbox is not flipped.
       const setReviewedStub = sinon.stub(element, 'setReviewed');
       const handleToggleSpy = sinon.spy(element, 'handleToggleFileReviewed');
-      assertIsDefined(element.reviewed);
-      element.reviewed.checked = false;
       assert.isFalse(handleToggleSpy.called);
       assert.isFalse(setReviewedStub.called);
 
@@ -791,10 +500,8 @@
         'wheatley.md': [createComment('c2', 21, 10, 'wheatley.md')],
       };
       element.changeComments = new ChangeComments(comment);
-      element.patchRange = {
-        basePatchNum: PARENT,
-        patchNum: 10 as RevisionPatchSetNum,
-      };
+      element.patchNum = 10 as RevisionPatchSetNum;
+      element.basePatchNum = PARENT;
       element.change = {
         ...createParsedChange(),
         _number: 42 as NumericChangeId,
@@ -810,23 +517,21 @@
       element.path = 'glados.txt';
       element.loggedIn = true;
       await element.updateComplete;
-      setUrlStub.reset();
+      navToDiffStub.reset();
 
       pressKey(element, 'N');
       await element.updateComplete;
-      assert.equal(setUrlStub.callCount, 1);
-      assert.equal(
-        setUrlStub.lastCall.firstArg,
-        '/c/test-project/+/42/10/wheatley.md#21'
-      );
+      assert.equal(navToDiffStub.callCount, 1);
+      assert.deepEqual(navToDiffStub.lastCall.args, [
+        {path: 'wheatley.md', lineNum: 21},
+      ]);
 
       element.path = 'wheatley.md'; // navigated to next file
 
       pressKey(element, 'N');
       await element.updateComplete;
 
-      assert.equal(setUrlStub.callCount, 2);
-      assert.equal(setUrlStub.lastCall.firstArg, '/c/test-project/+/42');
+      assert.equal(navToChangeStub.callCount, 1);
     });
 
     test('shift+x shortcut toggles all diff context', async () => {
@@ -838,114 +543,61 @@
     });
 
     test('diff against base', async () => {
-      element.patchRange = {
-        basePatchNum: 5 as BasePatchSetNum,
-        patchNum: 10 as RevisionPatchSetNum,
-      };
+      element.patchNum = 10 as RevisionPatchSetNum;
+      element.basePatchNum = 5 as BasePatchSetNum;
       await element.updateComplete;
       element.handleDiffAgainstBase();
-      assert.equal(
-        setUrlStub.lastCall.firstArg,
-        '/c/test-project/+/42/10/some/path.txt'
-      );
+      const expected = [{path: 'some/path.txt'}, 10, PARENT];
+      assert.deepEqual(navToDiffStub.lastCall.args, expected);
     });
 
     test('diff against latest', async () => {
       element.path = 'foo';
-      element.change = {
-        ...createParsedChange(),
-        revisions: createRevisions(12),
-      };
-      element.patchRange = {
-        basePatchNum: 5 as BasePatchSetNum,
-        patchNum: 10 as RevisionPatchSetNum,
-      };
+      element.latestPatchNum = 12 as PatchSetNumber;
+      element.patchNum = 10 as RevisionPatchSetNum;
+      element.basePatchNum = 5 as BasePatchSetNum;
       await element.updateComplete;
       element.handleDiffAgainstLatest();
-      assert.equal(
-        setUrlStub.lastCall.firstArg,
-        '/c/test-project/+/42/5..12/foo'
-      );
+      const expected = [{path: 'foo'}, 12, 5];
+      assert.deepEqual(navToDiffStub.lastCall.args, expected);
     });
 
     test('handleDiffBaseAgainstLeft', async () => {
       element.path = 'foo';
-      element.change = {
-        ...createParsedChange(),
-        revisions: createRevisions(10),
-      };
-      element.patchRange = {
+      element.latestPatchNum = 10 as PatchSetNumber;
+      element.patchNum = 3 as RevisionPatchSetNum;
+      element.basePatchNum = 1 as BasePatchSetNum;
+      viewModel.setState({
+        ...createDiffViewState(),
         patchNum: 3 as RevisionPatchSetNum,
         basePatchNum: 1 as BasePatchSetNum,
-      };
-      element.viewState = {
-        view: GerritView.DIFF,
-        changeNum: 42 as NumericChangeId,
-        patchNum: 3 as RevisionPatchSetNum,
-        basePatchNum: 1 as BasePatchSetNum,
-        path: 'foo',
-      };
+        diffView: {path: 'foo'},
+      });
       await element.updateComplete;
       element.handleDiffBaseAgainstLeft();
-      assert.equal(setUrlStub.lastCall.firstArg, '/c/test-project/+/42/1/foo');
-    });
-
-    test('handleDiffBaseAgainstLeft when initially navigating to a comment', () => {
-      element.change = {
-        ...createParsedChange(),
-        revisions: createRevisions(10),
-      };
-      element.patchRange = {
-        patchNum: 3 as RevisionPatchSetNum,
-        basePatchNum: 1 as BasePatchSetNum,
-      };
-      sinon.stub(element, 'viewStateChanged');
-      element.viewState = {
-        commentLink: true,
-        view: GerritView.DIFF,
-        changeNum: 42 as NumericChangeId,
-      };
-      element.focusLineNum = 10;
-      element.handleDiffBaseAgainstLeft();
-      assert.equal(
-        setUrlStub.lastCall.firstArg,
-        '/c/test-project/+/42/1/some/path.txt#10'
-      );
+      const expected = [{path: 'foo'}, 1, PARENT];
+      assert.deepEqual(navToDiffStub.lastCall.args, expected);
     });
 
     test('handleDiffRightAgainstLatest', async () => {
       element.path = 'foo';
-      element.change = {
-        ...createParsedChange(),
-        revisions: createRevisions(10),
-      };
-      element.patchRange = {
-        basePatchNum: 1 as BasePatchSetNum,
-        patchNum: 3 as RevisionPatchSetNum,
-      };
+      element.latestPatchNum = 10 as PatchSetNumber;
+      element.patchNum = 3 as RevisionPatchSetNum;
+      element.basePatchNum = 1 as BasePatchSetNum;
       await element.updateComplete;
       element.handleDiffRightAgainstLatest();
-      assert.equal(
-        setUrlStub.lastCall.firstArg,
-        '/c/test-project/+/42/3..10/foo'
-      );
+      const expected = [{path: 'foo'}, 10, 3];
+      assert.deepEqual(navToDiffStub.lastCall.args, expected);
     });
 
     test('handleDiffBaseAgainstLatest', async () => {
-      element.change = {
-        ...createParsedChange(),
-        revisions: createRevisions(10),
-      };
-      element.patchRange = {
-        basePatchNum: 1 as BasePatchSetNum,
-        patchNum: 3 as RevisionPatchSetNum,
-      };
+      element.latestPatchNum = 10 as PatchSetNumber;
+      element.patchNum = 3 as RevisionPatchSetNum;
+      element.basePatchNum = 1 as BasePatchSetNum;
       await element.updateComplete;
       element.handleDiffBaseAgainstLatest();
-      assert.equal(
-        setUrlStub.lastCall.firstArg,
-        '/c/test-project/+/42/10/some/path.txt'
-      );
+      const expected = [{path: 'some/path.txt'}, 10, PARENT];
+      assert.deepEqual(navToDiffStub.lastCall.args, expected);
     });
 
     test('A fires an error event when not logged in', async () => {
@@ -954,16 +606,14 @@
       element.addEventListener('show-auth-required', loggedInErrorSpy);
       pressKey(element, 'a');
       await element.updateComplete;
-      assert.isFalse(setUrlStub.calledOnce);
+      assert.isFalse(navToDiffStub.calledOnce);
       assert.isTrue(loggedInErrorSpy.called);
     });
 
     test('A navigates to change with logged in', async () => {
       element.changeNum = 42 as NumericChangeId;
-      element.patchRange = {
-        basePatchNum: 5 as BasePatchSetNum,
-        patchNum: 10 as RevisionPatchSetNum,
-      };
+      element.patchNum = 10 as RevisionPatchSetNum;
+      element.basePatchNum = 5 as BasePatchSetNum;
       element.change = {
         ...createParsedChange(),
         _number: 42 as NumericChangeId,
@@ -976,25 +626,20 @@
       await element.updateComplete;
       const loggedInErrorSpy = sinon.spy();
       element.addEventListener('show-auth-required', loggedInErrorSpy);
-      setUrlStub.reset();
+      navToDiffStub.reset();
 
       pressKey(element, 'a');
 
       await element.updateComplete;
-      assert.equal(setUrlStub.callCount, 1);
-      assert.equal(
-        setUrlStub.lastCall.firstArg,
-        '/c/test-project/+/42/5..10?openReplyDialog=true'
-      );
+      assert.isTrue(navToChangeStub.calledOnce);
+      assert.deepEqual(navToChangeStub.lastCall.args, [true]);
       assert.isFalse(loggedInErrorSpy.called);
     });
 
     test('A navigates to change with old patch number with logged in', async () => {
       element.changeNum = 42 as NumericChangeId;
-      element.patchRange = {
-        basePatchNum: PARENT,
-        patchNum: 1 as RevisionPatchSetNum,
-      };
+      element.patchNum = 1 as RevisionPatchSetNum;
+      element.basePatchNum = PARENT;
       element.change = {
         ...createParsedChange(),
         _number: 42 as NumericChangeId,
@@ -1008,20 +653,15 @@
       element.addEventListener('show-auth-required', loggedInErrorSpy);
       pressKey(element, 'a');
       await element.updateComplete;
-      assert.isTrue(setUrlStub.calledOnce);
-      assert.equal(
-        setUrlStub.lastCall.firstArg,
-        '/c/test-project/+/42/1?openReplyDialog=true'
-      );
+      assert.isTrue(navToChangeStub.calledOnce);
+      assert.deepEqual(navToChangeStub.lastCall.args, [true]);
       assert.isFalse(loggedInErrorSpy.called);
     });
 
     test('keyboard shortcuts with patch range', () => {
       element.changeNum = 42 as NumericChangeId;
-      element.patchRange = {
-        basePatchNum: 5 as BasePatchSetNum,
-        patchNum: 10 as RevisionPatchSetNum,
-      };
+      element.patchNum = 10 as RevisionPatchSetNum;
+      element.basePatchNum = 5 as BasePatchSetNum;
       element.change = {
         ...createParsedChange(),
         _number: 42 as NumericChangeId,
@@ -1038,40 +678,31 @@
       element.path = 'glados.txt';
 
       pressKey(element, 'u');
-      assert.equal(setUrlStub.callCount, 1);
-      assert.equal(setUrlStub.lastCall.firstArg, '/c/test-project/+/42/5..10');
+      assert.equal(navToChangeStub.callCount, 1);
 
       pressKey(element, ']');
-      assert.isTrue(element.loading);
-      assert.equal(setUrlStub.callCount, 2);
-      assert.equal(
-        setUrlStub.lastCall.firstArg,
-        '/c/test-project/+/42/5..10/wheatley.md'
-      );
+      assert.equal(navToDiffStub.callCount, 1);
+      assert.deepEqual(navToDiffStub.lastCall.args, [
+        {path: 'wheatley.md', lineNum: undefined},
+      ]);
       element.path = 'wheatley.md';
 
       pressKey(element, '[');
-      assert.isTrue(element.loading);
-      assert.equal(setUrlStub.callCount, 3);
-      assert.equal(
-        setUrlStub.lastCall.firstArg,
-        '/c/test-project/+/42/5..10/glados.txt'
-      );
+      assert.equal(navToDiffStub.callCount, 2);
+      assert.deepEqual(navToDiffStub.lastCall.args, [
+        {path: 'glados.txt', lineNum: undefined},
+      ]);
       element.path = 'glados.txt';
 
       pressKey(element, '[');
-      assert.isTrue(element.loading);
-      assert.equal(setUrlStub.callCount, 4);
-      assert.equal(
-        setUrlStub.lastCall.firstArg,
-        '/c/test-project/+/42/5..10/chell.go'
-      );
+      assert.equal(navToDiffStub.callCount, 3);
+      assert.deepEqual(navToDiffStub.lastCall.args, [
+        {path: 'chell.go', lineNum: undefined},
+      ]);
       element.path = 'chell.go';
 
       pressKey(element, '[');
-      assert.isTrue(element.loading);
-      assert.equal(setUrlStub.callCount, 5);
-      assert.equal(setUrlStub.lastCall.firstArg, '/c/test-project/+/42/5..10');
+      assert.equal(navToChangeStub.callCount, 2);
 
       assertIsDefined(element.downloadModal);
       const downloadModalStub = sinon.stub(element.downloadModal, 'showModal');
@@ -1079,12 +710,10 @@
       assert.isTrue(downloadModalStub.called);
     });
 
-    test('keyboard shortcuts with old patch number', () => {
+    test('keyboard shortcuts with old patch number', async () => {
       element.changeNum = 42 as NumericChangeId;
-      element.patchRange = {
-        basePatchNum: PARENT,
-        patchNum: 1 as RevisionPatchSetNum,
-      };
+      element.patchNum = 1 as RevisionPatchSetNum;
+      element.basePatchNum = PARENT;
       element.change = {
         ...createParsedChange(),
         _number: 42 as NumericChangeId,
@@ -1101,53 +730,57 @@
       element.path = 'glados.txt';
 
       pressKey(element, 'u');
-      assert.isTrue(setUrlStub.calledOnce);
-      assert.equal(setUrlStub.lastCall.firstArg, '/c/test-project/+/42/1');
+      assert.isTrue(navToChangeStub.calledOnce);
 
       pressKey(element, ']');
-      assert.equal(
-        setUrlStub.lastCall.firstArg,
-        '/c/test-project/+/42/1/wheatley.md'
-      );
+      assert.deepEqual(navToDiffStub.lastCall.args, [
+        {path: 'wheatley.md', lineNum: undefined},
+      ]);
       element.path = 'wheatley.md';
 
       pressKey(element, '[');
-      assert.equal(
-        setUrlStub.lastCall.firstArg,
-        '/c/test-project/+/42/1/glados.txt'
-      );
+      assert.deepEqual(navToDiffStub.lastCall.args, [
+        {path: 'glados.txt', lineNum: undefined},
+      ]);
       element.path = 'glados.txt';
 
       pressKey(element, '[');
-      assert.equal(
-        setUrlStub.lastCall.firstArg,
-        '/c/test-project/+/42/1/chell.go'
-      );
-      element.path = 'chell.go';
+      assert.deepEqual(navToDiffStub.lastCall.args, [
+        {path: 'chell.go', lineNum: undefined},
+      ]);
 
-      setUrlStub.reset();
+      element.path = 'chell.go';
+      await element.updateComplete;
+      navToDiffStub.reset();
       pressKey(element, '[');
-      assert.isTrue(setUrlStub.calledOnce);
-      assert.equal(setUrlStub.lastCall.firstArg, '/c/test-project/+/42/1');
+      assert.equal(navToChangeStub.callCount, 2);
+    });
+
+    test('reloadDiff is called when patchNum changes', async () => {
+      const reloadStub = sinon.stub(element, 'reloadDiff');
+      element.patchNum = 5 as RevisionPatchSetNum;
+      await element.updateComplete;
+      assert.isTrue(reloadStub.called);
+    });
+
+    test('initializePositions is called when view becomes active', async () => {
+      const reloadStub = sinon.stub(element, 'reloadDiff');
+      const initializeStub = sinon.stub(element, 'initializePositions');
+
+      element.isActiveChildView = false;
+      await element.updateComplete;
+      element.isActiveChildView = true;
+      await element.updateComplete;
+
+      assert.isTrue(initializeStub.calledOnce);
+      assert.isFalse(reloadStub.called);
     });
 
     test('edit should redirect to edit page', async () => {
       element.loggedIn = true;
       element.path = 't.txt';
-      element.patchRange = {
-        basePatchNum: PARENT,
-        patchNum: 1 as RevisionPatchSetNum,
-      };
-      element.change = {
-        ...createParsedChange(),
-        _number: 42 as NumericChangeId,
-        project: 'gerrit' as RepoName,
-        status: ChangeStatus.NEW,
-        revisions: {
-          a: createRevision(1),
-          b: createRevision(2),
-        },
-      };
+      element.patchNum = 1 as RevisionPatchSetNum;
+      element.basePatchNum = PARENT;
       await element.updateComplete;
       const editBtn = queryAndAssert<GrButton>(
         element,
@@ -1155,28 +788,18 @@
       );
       assert.isTrue(!!editBtn);
       editBtn.click();
-      assert.equal(setUrlStub.callCount, 1);
-      assert.equal(setUrlStub.lastCall.firstArg, '/c/gerrit/+/42/1/t.txt,edit');
+      assert.equal(navToEditStub.callCount, 1);
+      assert.deepEqual(navToEditStub.lastCall.args, [
+        {path: 't.txt', lineNum: undefined},
+      ]);
     });
 
     test('edit should redirect to edit page with line number', async () => {
       const lineNumber = 42;
       element.loggedIn = true;
       element.path = 't.txt';
-      element.patchRange = {
-        basePatchNum: PARENT,
-        patchNum: 1 as RevisionPatchSetNum,
-      };
-      element.change = {
-        ...createParsedChange(),
-        _number: 42 as NumericChangeId,
-        project: 'gerrit' as RepoName,
-        status: ChangeStatus.NEW,
-        revisions: {
-          a: createRevision(1),
-          b: createRevision(2),
-        },
-      };
+      element.patchNum = 1 as RevisionPatchSetNum;
+      element.basePatchNum = PARENT;
       assertIsDefined(element.cursor);
       sinon
         .stub(element.cursor, 'getAddress')
@@ -1188,11 +811,10 @@
       );
       assert.isTrue(!!editBtn);
       editBtn.click();
-      assert.equal(setUrlStub.callCount, 1);
-      assert.equal(
-        setUrlStub.lastCall.firstArg,
-        '/c/gerrit/+/42/1/t.txt,edit#42'
-      );
+      assert.equal(navToEditStub.callCount, 1);
+      assert.deepEqual(navToEditStub.lastCall.args, [
+        {path: 't.txt', lineNum: 42},
+      ]);
     });
 
     async function isEditVisibile({
@@ -1204,10 +826,8 @@
     }): Promise<boolean> {
       element.loggedIn = loggedIn;
       element.path = 't.txt';
-      element.patchRange = {
-        basePatchNum: PARENT,
-        patchNum: 1 as RevisionPatchSetNum,
-      };
+      element.patchNum = 1 as RevisionPatchSetNum;
+      element.basePatchNum = PARENT;
       element.change = {
         ...createParsedChange(),
         _number: 42 as NumericChangeId,
@@ -1304,16 +924,10 @@
     });
 
     suite('url parameters', () => {
-      setup(() => {
-        sinon.stub(element, 'fetchFiles');
-      });
-
       test('_formattedFiles', () => {
         element.changeNum = 42 as NumericChangeId;
-        element.patchRange = {
-          basePatchNum: PARENT,
-          patchNum: 10 as RevisionPatchSetNum,
-        };
+        element.patchNum = 10 as RevisionPatchSetNum;
+        element.basePatchNum = PARENT;
         element.change = {
           ...createParsedChange(),
           _number: 42 as NumericChangeId,
@@ -1386,18 +1000,19 @@
       });
 
       test('prev/up/next links', async () => {
-        element.changeNum = 42 as NumericChangeId;
-        element.patchRange = {
-          basePatchNum: PARENT,
-          patchNum: 10 as RevisionPatchSetNum,
-        };
-        element.change = {
+        viewModel.setState({
+          ...createDiffViewState(),
+        });
+        const change = {
           ...createParsedChange(),
           _number: 42 as NumericChangeId,
           revisions: {
             a: createRevision(10),
           },
         };
+        changeModel.updateStateChange(change);
+        await element.updateComplete;
+
         element.files = getFilesFromFileList([
           'chell.go',
           'glados.txt',
@@ -1417,24 +1032,30 @@
           linkEls[2].getAttribute('href'),
           '/c/test-project/+/42/10/wheatley.md'
         );
+
         element.path = 'wheatley.md';
         await element.updateComplete;
+
         assert.equal(
           linkEls[0].getAttribute('href'),
           '/c/test-project/+/42/10/glados.txt'
         );
         assert.equal(linkEls[1].getAttribute('href'), '/c/test-project/+/42');
         assert.equal(linkEls[2].getAttribute('href'), '/c/test-project/+/42');
+
         element.path = 'chell.go';
         await element.updateComplete;
+
         assert.equal(linkEls[0].getAttribute('href'), '/c/test-project/+/42');
         assert.equal(linkEls[1].getAttribute('href'), '/c/test-project/+/42');
         assert.equal(
           linkEls[2].getAttribute('href'),
           '/c/test-project/+/42/10/glados.txt'
         );
+
         element.path = 'not_a_real_file';
         await element.updateComplete;
+
         assert.equal(
           linkEls[0].getAttribute('href'),
           '/c/test-project/+/42/10/wheatley.md'
@@ -1447,26 +1068,30 @@
       });
 
       test('prev/up/next links with patch range', async () => {
-        element.changeNum = 42 as NumericChangeId;
-        element.patchRange = {
+        viewModel.setState({
+          ...createDiffViewState(),
           basePatchNum: 5 as BasePatchSetNum,
           patchNum: 10 as RevisionPatchSetNum,
-        };
-        element.change = {
+          diffView: {path: 'glados.txt'},
+        });
+        const change = {
           ...createParsedChange(),
           _number: 42 as NumericChangeId,
           revisions: {
             a: createRevision(5),
             b: createRevision(10),
+            c: createRevision(12),
           },
         };
+        changeModel.updateStateChange(change);
         element.files = getFilesFromFileList([
           'chell.go',
           'glados.txt',
           'wheatley.md',
         ]);
-        element.path = 'glados.txt';
-        await element.updateComplete;
+        await waitUntil(() => element.path === 'glados.txt');
+        await waitUntil(() => element.patchRange?.patchNum === 10);
+
         const linkEls = queryAll(element, '.navLink');
         assert.equal(linkEls.length, 3);
         assert.equal(
@@ -1481,8 +1106,10 @@
           linkEls[2].getAttribute('href'),
           '/c/test-project/+/42/5..10/wheatley.md'
         );
-        element.path = 'wheatley.md';
-        await element.updateComplete;
+
+        viewModel.updateState({diffView: {path: 'wheatley.md'}});
+        await waitUntil(() => element.path === 'wheatley.md');
+
         assert.equal(
           linkEls[0].getAttribute('href'),
           '/c/test-project/+/42/5..10/glados.txt'
@@ -1495,8 +1122,10 @@
           linkEls[2].getAttribute('href'),
           '/c/test-project/+/42/5..10'
         );
-        element.path = 'chell.go';
-        await element.updateComplete;
+
+        viewModel.updateState({diffView: {path: 'chell.go'}});
+        await waitUntil(() => element.path === 'chell.go');
+
         assert.equal(
           linkEls[0].getAttribute('href'),
           '/c/test-project/+/42/5..10'
@@ -1513,32 +1142,24 @@
     });
 
     test('handlePatchChange calls setUrl correctly', async () => {
-      element.change = {
-        ...createParsedChange(),
-        _number: 321 as NumericChangeId,
-        project: 'foo/bar' as RepoName,
-      };
       element.path = 'path/to/file.txt';
-
-      element.patchRange = {
-        basePatchNum: PARENT,
-        patchNum: 3 as RevisionPatchSetNum,
-      };
+      element.patchNum = 3 as RevisionPatchSetNum;
+      element.basePatchNum = PARENT;
       await element.updateComplete;
 
       const detail = {
         basePatchNum: PARENT,
         patchNum: 1 as RevisionPatchSetNum,
       };
-
       queryAndAssert(element, '#rangeSelect').dispatchEvent(
         new CustomEvent('patch-range-change', {detail, bubbles: false})
       );
 
-      assert.equal(
-        setUrlStub.lastCall.firstArg,
-        '/c/foo/bar/+/321/1/path/to/file.txt'
-      );
+      assert.deepEqual(navToDiffStub.lastCall.args, [
+        {path: element.path},
+        detail.patchNum,
+        detail.basePatchNum,
+      ]);
     });
 
     test(
@@ -1559,23 +1180,13 @@
           manual_review: true,
         };
         userModel.setDiffPreferences(diffPreferences);
+        viewModel.updateState({diffView: {path: 'wheatley.md'}});
         changeModel.setState({
           change: createParsedChange(),
-          diffPath: '/COMMIT_MSG',
           reviewedFiles: [],
           loadingStatus: LoadingStatus.LOADED,
         });
 
-        testResolver(routerModelToken).setState({
-          changeNum: TEST_NUMERIC_CHANGE_ID,
-          view: GerritView.DIFF,
-          patchNum: 2 as RevisionPatchSetNum,
-        });
-        element.patchRange = {
-          patchNum: 2 as RevisionPatchSetNum,
-          basePatchNum: 1 as BasePatchSetNum,
-        };
-
         await waitUntil(() => setReviewedStatusStub.called);
 
         assert.isFalse(setReviewedFileStatusStub.called);
@@ -1601,55 +1212,39 @@
         manual_review: false,
       };
       userModel.setDiffPreferences(diffPreferences);
+      viewModel.updateState({diffView: {path: 'wheatley.md'}});
       changeModel.setState({
         change: createParsedChange(),
-        diffPath: '/COMMIT_MSG',
         reviewedFiles: [],
         loadingStatus: LoadingStatus.LOADED,
       });
 
-      testResolver(routerModelToken).setState({
-        changeNum: TEST_NUMERIC_CHANGE_ID,
-        view: GerritView.DIFF,
-        patchNum: 22 as RevisionPatchSetNum,
-      });
-      element.patchRange = {
-        patchNum: 2 as RevisionPatchSetNum,
-        basePatchNum: 1 as BasePatchSetNum,
-      };
-
       await waitUntil(() => setReviewedFileStatusStub.called);
 
       assert.isTrue(setReviewedFileStatusStub.called);
     });
 
     test('file review status', async () => {
+      const saveReviewedStub = sinon
+        .stub(changeModel, 'setReviewedFilesStatus')
+        .callsFake(() => Promise.resolve());
+      userModel.setDiffPreferences(createDefaultDiffPrefs());
+      viewModel.updateState({
+        patchNum: 1 as RevisionPatchSetNum,
+        basePatchNum: PARENT,
+        diffView: {path: '/COMMIT_MSG'},
+      });
       changeModel.setState({
         change: createParsedChange(),
-        diffPath: '/COMMIT_MSG',
         reviewedFiles: [],
         loadingStatus: LoadingStatus.LOADED,
       });
       element.loggedIn = true;
-      const saveReviewedStub = sinon
-        .stub(changeModel, 'setReviewedFilesStatus')
-        .callsFake(() => Promise.resolve());
+      await waitUntil(() => element.patchRange?.patchNum === 1);
+      await element.updateComplete;
       assertIsDefined(element.diffHost);
       sinon.stub(element.diffHost, 'reload');
 
-      userModel.setDiffPreferences(createDefaultDiffPrefs());
-
-      testResolver(routerModelToken).setState({
-        changeNum: TEST_NUMERIC_CHANGE_ID,
-        view: GerritView.DIFF,
-        patchNum: 2 as RevisionPatchSetNum,
-      });
-
-      element.patchRange = {
-        patchNum: 2 as RevisionPatchSetNum,
-        basePatchNum: 1 as BasePatchSetNum,
-      };
-
       await waitUntil(() => saveReviewedStub.called);
 
       changeModel.updateStateFileReviewed('/COMMIT_MSG', true);
@@ -1657,13 +1252,13 @@
 
       const reviewedStatusCheckBox = queryAndAssert<HTMLInputElement>(
         element,
-        'input[type="checkbox"]'
+        'input#reviewed'
       );
 
       assert.isTrue(reviewedStatusCheckBox.checked);
       assert.deepEqual(saveReviewedStub.lastCall.args, [
         42,
-        2,
+        1,
         '/COMMIT_MSG',
         true,
       ]);
@@ -1672,7 +1267,7 @@
       assert.isFalse(reviewedStatusCheckBox.checked);
       assert.deepEqual(saveReviewedStub.lastCall.args, [
         42,
-        2,
+        1,
         '/COMMIT_MSG',
         false,
       ]);
@@ -1684,18 +1279,17 @@
       assert.isTrue(reviewedStatusCheckBox.checked);
       assert.deepEqual(saveReviewedStub.lastCall.args, [
         42,
-        2,
+        1,
         '/COMMIT_MSG',
         true,
       ]);
 
       const callCount = saveReviewedStub.callCount;
 
-      element.viewState = {
-        view: GerritView.DIFF,
-        changeNum: 42 as NumericChangeId,
+      viewModel.setState({
+        ...createDiffViewState(),
         repo: 'test' as RepoName,
-      };
+      });
       await element.updateComplete;
 
       // saveReviewedState observer observes viewState, but should not fire when
@@ -1703,20 +1297,18 @@
       assert.equal(saveReviewedStub.callCount, callCount);
     });
 
-    test('file review status with edit loaded', async () => {
+    test('do not set file review status for EDIT patchset', async () => {
       const saveReviewedStub = sinon.stub(
         changeModel,
         'setReviewedFilesStatus'
       );
 
-      element.patchRange = {
-        basePatchNum: 1 as BasePatchSetNum,
-        patchNum: EDIT,
-      };
+      element.patchNum = EDIT;
+      element.basePatchNum = 1 as BasePatchSetNum;
       await waitEventLoop();
 
-      assert.isTrue(element.computeEditMode());
       element.setReviewed(true);
+
       assert.isFalse(saveReviewedStub.called);
     });
 
@@ -1725,14 +1317,7 @@
       sinon.stub(element.diffHost, 'reload');
       const initLineStub = sinon.stub(element, 'initLineOfInterestAndCursor');
 
-      element.loggedIn = true;
-      element.viewState = {
-        view: GerritView.DIFF,
-        changeNum: 42 as NumericChangeId,
-        patchNum: 2 as RevisionPatchSetNum,
-        basePatchNum: 1 as BasePatchSetNum,
-        path: '/COMMIT_MSG',
-      };
+      element.focusLineNum = 123;
 
       await element.updateComplete;
       await waitEventLoop();
@@ -1780,115 +1365,56 @@
       assert.isTrue(diffModeSelector.classList.contains('hide'));
     });
 
-    suite('commitRange', () => {
-      const change: ParsedChangeInfo = {
-        ...createParsedChange(),
-        _number: 42 as NumericChangeId,
-        revisions: {
-          'commit-sha-1': {
-            ...createRevision(1),
-            commit: {
-              ...createCommit(),
-              parents: [{subject: 's1', commit: 'sha-1-parent' as CommitId}],
-            },
-          },
-          'commit-sha-2': createRevision(2),
-          'commit-sha-3': createRevision(3),
-          'commit-sha-4': createRevision(4),
-          'commit-sha-5': {
-            ...createRevision(5),
-            commit: {
-              ...createCommit(),
-              parents: [{subject: 's5', commit: 'sha-5-parent' as CommitId}],
-            },
-          },
-        },
-      };
-      setup(async () => {
-        assertIsDefined(element.diffHost);
-        sinon.stub(element.diffHost, 'reload');
-        sinon.stub(element, 'initCursor');
-        element.change = change;
-        await element.updateComplete;
-        await element.diffHost.updateComplete;
-      });
-
-      test('uses the patchNum and basePatchNum ', async () => {
-        element.viewState = {
-          view: GerritView.DIFF,
-          changeNum: 42 as NumericChangeId,
-          patchNum: 4 as RevisionPatchSetNum,
-          basePatchNum: 2 as BasePatchSetNum,
-          path: '/COMMIT_MSG',
-        };
-        element.change = change;
-        await element.updateComplete;
-        await waitEventLoop();
-        assert.deepEqual(element.commitRange, {
-          baseCommit: 'commit-sha-2' as CommitId,
-          commit: 'commit-sha-4' as CommitId,
-        });
-      });
-
-      test('uses the parent when there is no base patch num ', async () => {
-        element.viewState = {
-          view: GerritView.DIFF,
-          changeNum: 42 as NumericChangeId,
-          patchNum: 5 as RevisionPatchSetNum,
-          path: '/COMMIT_MSG',
-        };
-        element.change = change;
-        await element.updateComplete;
-        await waitEventLoop();
-        assert.deepEqual(element.commitRange, {
-          commit: 'commit-sha-5' as CommitId,
-          baseCommit: 'sha-5-parent' as CommitId,
-        });
-      });
-    });
-
     test('initCursor', () => {
       assertIsDefined(element.cursor);
       assert.isNotOk(element.cursor.initialLineNumber);
 
       // Does nothing when viewState specify no cursor address:
-      element.initCursor(false);
+      element.leftSide = false;
+      element.initCursor();
       assert.isNotOk(element.cursor.initialLineNumber);
 
       // Does nothing when viewState specify side but no number:
-      element.initCursor(true);
+      element.leftSide = true;
+      element.initCursor();
       assert.isNotOk(element.cursor.initialLineNumber);
 
       // Revision hash: specifies lineNum but not side.
 
       element.focusLineNum = 234;
-      element.initCursor(false);
+      element.leftSide = false;
+      element.initCursor();
       assert.equal(element.cursor.initialLineNumber, 234);
       assert.equal(element.cursor.side, Side.RIGHT);
 
       // Base hash: specifies lineNum and side.
       element.focusLineNum = 345;
-      element.initCursor(true);
+      element.leftSide = true;
+      element.initCursor();
       assert.equal(element.cursor.initialLineNumber, 345);
       assert.equal(element.cursor.side, Side.LEFT);
 
       // Specifies right side:
       element.focusLineNum = 123;
-      element.initCursor(false);
+      element.leftSide = false;
+      element.initCursor();
       assert.equal(element.cursor.initialLineNumber, 123);
       assert.equal(element.cursor.side, Side.RIGHT);
     });
 
     test('getLineOfInterest', () => {
-      assert.isUndefined(element.getLineOfInterest(false));
+      element.leftSide = false;
+      assert.isUndefined(element.getLineOfInterest());
 
       element.focusLineNum = 12;
-      let result = element.getLineOfInterest(false);
+      element.leftSide = false;
+      let result = element.getLineOfInterest();
       assert.isOk(result);
       assert.equal(result!.lineNum, 12);
       assert.equal(result!.side, Side.RIGHT);
 
-      result = element.getLineOfInterest(true);
+      element.leftSide = true;
+      result = element.getLineOfInterest();
       assert.isOk(result);
       assert.equal(result!.lineNum, 12);
       assert.equal(result!.side, Side.LEFT);
@@ -1907,10 +1433,8 @@
         _number: 321 as NumericChangeId,
         project: 'foo/bar' as RepoName,
       };
-      element.patchRange = {
-        basePatchNum: 3 as BasePatchSetNum,
-        patchNum: 5 as RevisionPatchSetNum,
-      };
+      element.patchNum = 5 as RevisionPatchSetNum;
+      element.basePatchNum = 3 as BasePatchSetNum;
       const e = {detail: {number: 123, side: Side.RIGHT}} as CustomEvent;
 
       element.onLineSelected(e);
@@ -1931,10 +1455,8 @@
         _number: 321 as NumericChangeId,
         project: 'foo/bar' as RepoName,
       };
-      element.patchRange = {
-        basePatchNum: 3 as BasePatchSetNum,
-        patchNum: 5 as RevisionPatchSetNum,
-      };
+      element.patchNum = 5 as RevisionPatchSetNum;
+      element.basePatchNum = 3 as BasePatchSetNum;
       const e = {detail: {number: 123, side: Side.LEFT}} as CustomEvent;
 
       element.onLineSelected(e);
@@ -1965,199 +1487,116 @@
       });
     });
 
-    suite('initPatchRange', () => {
-      setup(async () => {
-        getDiffRestApiStub.returns(Promise.resolve(createDiff()));
-        element.viewState = {
-          view: GerritView.DIFF,
-          changeNum: 42 as NumericChangeId,
-          patchNum: 3 as RevisionPatchSetNum,
-          path: 'abcd',
-        };
-        await element.updateComplete;
-      });
-      test('empty', () => {
-        sinon.stub(element, 'getPaths').returns({});
-        element.initPatchRange();
-        assert.equal(Object.keys(element.commentMap ?? {}).length, 0);
-      });
-
-      test('has paths', () => {
-        sinon.stub(element, 'fetchFiles');
-        sinon.stub(element, 'getPaths').returns({
-          'path/to/file/one.cpp': true,
-          'path-to/file/two.py': true,
-        });
-        element.changeNum = 42 as NumericChangeId;
-        element.patchRange = {
-          basePatchNum: 3 as BasePatchSetNum,
-          patchNum: 5 as RevisionPatchSetNum,
-        };
-        element.initPatchRange();
-        assert.deepEqual(Object.keys(element.commentMap ?? {}), [
-          'path/to/file/one.cpp',
-          'path-to/file/two.py',
-        ]);
-      });
-    });
-
-    suite('computeCommentSkips', () => {
+    suite('findFileWithComment', () => {
       test('empty file list', () => {
-        const commentMap = {
-          'path/one.jpg': true,
-          'path/three.wav': true,
-        };
-        const path = 'path/two.m4v';
-        const result = element.computeCommentSkips(commentMap, [], path);
-        assert.isOk(result);
-        assert.isNotOk(result!.previous);
-        assert.isNotOk(result!.next);
+        element.changeComments = new ChangeComments({
+          'path/one.jpg': [createComment('c1', 1, 1, 'path/one.jpg')],
+          'path/three.wav': [createComment('c1', 1, 1, 'path/three.wav')],
+        });
+        element.path = 'path/two.m4v';
+        assert.isUndefined(element.findFileWithComment(-1));
+        assert.isUndefined(element.findFileWithComment(1));
       });
 
       test('finds skips', () => {
         const fileList = ['path/one.jpg', 'path/two.m4v', 'path/three.wav'];
-        let path = fileList[1];
-        const commentMap: CommentMap = {};
-        commentMap[fileList[0]] = true;
-        commentMap[fileList[1]] = false;
-        commentMap[fileList[2]] = true;
+        element.files = {sortedPaths: fileList, changeFilesByPath: {}};
+        element.path = fileList[1];
+        element.changeComments = new ChangeComments({
+          'path/one.jpg': [createComment('c1', 1, 1, 'path/one.jpg')],
+          'path/three.wav': [createComment('c1', 1, 1, 'path/three.wav')],
+        });
 
-        let result = element.computeCommentSkips(commentMap, fileList, path);
-        assert.isOk(result);
-        assert.equal(result!.previous, fileList[0]);
-        assert.equal(result!.next, fileList[2]);
+        assert.equal(element.findFileWithComment(-1), fileList[0]);
+        assert.equal(element.findFileWithComment(1), fileList[2]);
 
-        commentMap[fileList[1]] = true;
+        element.changeComments = new ChangeComments({
+          'path/one.jpg': [createComment('c1', 1, 1, 'path/one.jpg')],
+          'path/two.m4v': [createComment('c1', 1, 1, 'path/two.m4v')],
+          'path/three.wav': [createComment('c1', 1, 1, 'path/three.wav')],
+        });
 
-        result = element.computeCommentSkips(commentMap, fileList, path);
-        assert.isOk(result);
-        assert.equal(result!.previous, fileList[0]);
-        assert.equal(result!.next, fileList[2]);
+        assert.equal(element.findFileWithComment(-1), fileList[0]);
+        assert.equal(element.findFileWithComment(1), fileList[2]);
 
-        path = fileList[0];
+        element.path = fileList[0];
 
-        result = element.computeCommentSkips(commentMap, fileList, path);
-        assert.isOk(result);
-        assert.isNull(result!.previous);
-        assert.equal(result!.next, fileList[1]);
+        assert.isUndefined(element.findFileWithComment(-1));
+        assert.equal(element.findFileWithComment(1), fileList[1]);
 
-        path = fileList[2];
+        element.path = fileList[2];
 
-        result = element.computeCommentSkips(commentMap, fileList, path);
-        assert.isOk(result);
-        assert.equal(result!.previous, fileList[1]);
-        assert.isNull(result!.next);
+        assert.equal(element.findFileWithComment(-1), fileList[1]);
+        assert.isUndefined(element.findFileWithComment(1));
       });
 
       suite('skip next/previous', () => {
-        let navToChangeStub: SinonStub;
-
         setup(() => {
-          navToChangeStub = sinon.stub(element, 'navToChangeView');
           element.files = getFilesFromFileList([
             'path/one.jpg',
             'path/two.m4v',
             'path/three.wav',
           ]);
-          element.patchRange = {
-            patchNum: 2 as RevisionPatchSetNum,
-            basePatchNum: 1 as BasePatchSetNum,
-          };
+          element.patchNum = 2 as RevisionPatchSetNum;
+          element.basePatchNum = 1 as BasePatchSetNum;
         });
 
-        suite('moveToPreviousFileWithComment', () => {
-          test('no skips', () => {
-            element.moveToPreviousFileWithComment();
-            assert.isFalse(navToChangeStub.called);
-            assert.isFalse(setUrlStub.called);
-          });
-
+        suite('moveToFileWithComment previous', () => {
           test('no previous', async () => {
-            const commentMap: CommentMap = {};
-            commentMap[element.files.sortedFileList[0]!] = false;
-            commentMap[element.files.sortedFileList[1]!] = false;
-            commentMap[element.files.sortedFileList[2]!] = true;
-            element.commentMap = commentMap;
-            element.path = element.files.sortedFileList[1];
+            element.changeComments = new ChangeComments({
+              'path/three.wav': [createComment('c1', 1, 1, 'path/three.wav')],
+            });
+            element.path = element.files.sortedPaths[1];
             await element.updateComplete;
 
-            element.moveToPreviousFileWithComment();
+            element.moveToFileWithComment(-1);
             assert.isTrue(navToChangeStub.calledOnce);
-            assert.isFalse(setUrlStub.called);
+            assert.isFalse(navToDiffStub.called);
           });
 
           test('w/ previous', async () => {
-            const commentMap: CommentMap = {};
-            commentMap[element.files.sortedFileList[0]!] = true;
-            commentMap[element.files.sortedFileList[1]!] = false;
-            commentMap[element.files.sortedFileList[2]!] = true;
-            element.commentMap = commentMap;
-            element.path = element.files.sortedFileList[1];
+            element.changeComments = new ChangeComments({
+              'path/one.jpg': [createComment('c1', 1, 1, 'path/one.jpg')],
+              'path/three.wav': [createComment('c1', 1, 1, 'path/three.wav')],
+            });
+            element.path = element.files.sortedPaths[1];
             await element.updateComplete;
 
-            element.moveToPreviousFileWithComment();
+            element.moveToFileWithComment(-1);
             assert.isFalse(navToChangeStub.called);
-            assert.isTrue(setUrlStub.calledOnce);
+            assert.isTrue(navToDiffStub.calledOnce);
           });
         });
 
-        suite('moveToNextFileWithComment', () => {
-          test('no skips', () => {
-            element.moveToNextFileWithComment();
-            assert.isFalse(navToChangeStub.called);
-            assert.isFalse(setUrlStub.called);
-          });
-
+        suite('moveToFileWithComment next', () => {
           test('no previous', async () => {
-            const commentMap: CommentMap = {};
-            commentMap[element.files.sortedFileList[0]!] = true;
-            commentMap[element.files.sortedFileList[1]!] = false;
-            commentMap[element.files.sortedFileList[2]!] = false;
-            element.commentMap = commentMap;
-            element.path = element.files.sortedFileList[1];
+            element.changeComments = new ChangeComments({
+              'path/one.jpg': [createComment('c1', 1, 1, 'path/one.jpg')],
+            });
+            element.path = element.files.sortedPaths[1];
             await element.updateComplete;
 
-            element.moveToNextFileWithComment();
+            element.moveToFileWithComment(1);
             assert.isTrue(navToChangeStub.calledOnce);
-            assert.isFalse(setUrlStub.called);
+            assert.isFalse(navToDiffStub.called);
           });
 
           test('w/ previous', async () => {
-            const commentMap: CommentMap = {};
-            commentMap[element.files.sortedFileList[0]!] = true;
-            commentMap[element.files.sortedFileList[1]!] = false;
-            commentMap[element.files.sortedFileList[2]!] = true;
-            element.commentMap = commentMap;
-            element.path = element.files.sortedFileList[1];
+            element.changeComments = new ChangeComments({
+              'path/one.jpg': [createComment('c1', 1, 1, 'path/one.jpg')],
+              'path/three.wav': [createComment('c1', 1, 1, 'path/three.wav')],
+            });
+            element.path = element.files.sortedPaths[1];
             await element.updateComplete;
 
-            element.moveToNextFileWithComment();
+            element.moveToFileWithComment(1);
             assert.isFalse(navToChangeStub.called);
-            assert.isTrue(setUrlStub.calledOnce);
+            assert.isTrue(navToDiffStub.calledOnce);
           });
         });
       });
     });
 
-    test('_computeEditMode', () => {
-      const callCompute = (range: PatchRange) => {
-        element.patchRange = range;
-        return element.computeEditMode();
-      };
-      assert.isFalse(
-        callCompute({
-          basePatchNum: PARENT,
-          patchNum: 1 as RevisionPatchSetNum,
-        })
-      );
-      assert.isTrue(
-        callCompute({
-          basePatchNum: 1 as BasePatchSetNum,
-          patchNum: EDIT,
-        })
-      );
-    });
-
     test('computeFileNum', () => {
       element.path = '/foo';
       assert.equal(
@@ -2224,15 +1663,18 @@
 
       test('reviewed checkbox', async () => {
         sinon.stub(element, 'handlePatchChange');
-        element.patchRange = createPatchRange();
-        await element.updateComplete;
-        assertIsDefined(element.reviewed);
-        // Reviewed checkbox should be shown.
-        assert.isTrue(isVisible(element.reviewed));
-        element.patchRange = {...element.patchRange, patchNum: EDIT};
+        element.patchNum = 1 as RevisionPatchSetNum;
+        element.basePatchNum = PARENT;
         await element.updateComplete;
 
-        assert.isFalse(isVisible(element.reviewed));
+        let checkbox = queryAndAssert(element, '#reviewed');
+        assert.isTrue(isVisible(checkbox));
+
+        element.patchNum = EDIT;
+        await element.updateComplete;
+
+        checkbox = queryAndAssert(element, '#reviewed');
+        assert.isFalse(isVisible(checkbox));
       });
     });
 
@@ -2380,45 +1822,39 @@
       sinon.stub(element, 'initLineOfInterestAndCursor');
 
       // Load file1
-      element.viewState = {
-        view: GerritView.DIFF,
+      viewModel.setState({
+        ...createDiffViewState(),
         patchNum: 1 as RevisionPatchSetNum,
-        changeNum: 101 as NumericChangeId,
         repo: 'test-project' as RepoName,
-        path: 'file1',
-      };
-      element.patchRange = {
-        patchNum: 1 as RevisionPatchSetNum,
-        basePatchNum: PARENT,
-      };
+        diffView: {path: 'file1'},
+      });
+      element.patchNum = 1 as RevisionPatchSetNum;
+      element.basePatchNum = PARENT;
       element.change = {
         ...createParsedChange(),
         revisions: createRevisions(1),
       };
       await element.updateComplete;
-      assert.isFalse(setUrlStub.called);
+      assert.isFalse(navToDiffStub.called);
 
       // Switch to file2
       element.handleFileChange(
         new CustomEvent('value-change', {detail: {value: 'file2'}})
       );
-      assert.isTrue(setUrlStub.calledOnce);
+      assert.isTrue(navToDiffStub.calledOnce);
 
       // This is to mock the param change triggered by above navigate
-      element.viewState = {
-        view: GerritView.DIFF,
+      viewModel.setState({
+        ...createDiffViewState(),
         patchNum: 1 as RevisionPatchSetNum,
-        changeNum: 101 as NumericChangeId,
         repo: 'test-project' as RepoName,
-        path: 'file2',
-      };
-      element.patchRange = {
-        patchNum: 1 as RevisionPatchSetNum,
-        basePatchNum: PARENT,
-      };
+        diffView: {path: 'file2'},
+      });
+      element.patchNum = 1 as RevisionPatchSetNum;
+      element.basePatchNum = PARENT;
 
       // No extra call
-      assert.isTrue(setUrlStub.calledOnce);
+      assert.isTrue(navToDiffStub.calledOnce);
     });
 
     test('_computeDownloadDropdownLinks', () => {
@@ -2440,10 +1876,8 @@
       element.change = createParsedChange();
       element.change.project = 'test' as RepoName;
       element.changeNum = 12 as NumericChangeId;
-      element.patchRange = {
-        patchNum: 1 as RevisionPatchSetNum,
-        basePatchNum: PARENT,
-      };
+      element.patchNum = 1 as RevisionPatchSetNum;
+      element.basePatchNum = PARENT;
       element.path = 'index.php';
       element.diff = createDiff();
       assert.deepEqual(element.computeDownloadDropdownLinks(), downloadLinks);
@@ -2472,10 +1906,8 @@
       element.change = createParsedChange();
       element.change.project = 'test' as RepoName;
       element.changeNum = 12 as NumericChangeId;
-      element.patchRange = {
-        patchNum: 3 as RevisionPatchSetNum,
-        basePatchNum: 2 as BasePatchSetNum,
-      };
+      element.patchNum = 3 as RevisionPatchSetNum;
+      element.basePatchNum = 2 as BasePatchSetNum;
       element.path = 'index.php';
       element.diff = diff;
       assert.deepEqual(element.computeDownloadDropdownLinks(), downloadLinks);
@@ -2539,49 +1971,4 @@
       );
     });
   });
-
-  suite('unmodified files with comments', () => {
-    let element: GrDiffView;
-
-    setup(async () => {
-      const changedFiles = {
-        'file1.txt': createFileInfo(),
-        'a/b/test.c': createFileInfo(),
-      };
-      stubRestApi('getConfig').returns(Promise.resolve(createServerInfo()));
-      stubRestApi('getProjectConfig').returns(Promise.resolve(createConfig()));
-      stubRestApi('getChangeFiles').returns(Promise.resolve(changedFiles));
-      stubRestApi('saveFileReviewed').returns(Promise.resolve(new Response()));
-      stubRestApi('getDiffComments').returns(Promise.resolve({}));
-      stubRestApi('getDiffRobotComments').returns(Promise.resolve({}));
-      stubRestApi('getDiffDrafts').returns(Promise.resolve({}));
-      stubRestApi('getReviewedFiles').returns(Promise.resolve([]));
-      element = await fixture(html`<gr-diff-view></gr-diff-view>`);
-      element.changeNum = 42 as NumericChangeId;
-    });
-
-    test('fetchFiles add files with comments without changes', () => {
-      element.patchRange = {
-        basePatchNum: 5 as BasePatchSetNum,
-        patchNum: 10 as RevisionPatchSetNum,
-      };
-      element.changeComments = {
-        getPaths: sinon.stub().returns({
-          'file2.txt': {},
-          'file1.txt': {},
-        }),
-      } as unknown as ChangeComments;
-      element.changeNum = 23 as NumericChangeId;
-      return element.fetchFiles().then(() => {
-        assert.deepEqual(element.files, {
-          sortedFileList: ['a/b/test.c', 'file1.txt', 'file2.txt'],
-          changeFilesByPath: {
-            'file1.txt': createFileInfo(),
-            'file2.txt': {status: 'U'} as FileInfo,
-            'a/b/test.c': createFileInfo(),
-          },
-        });
-      });
-    });
-  });
 });
diff --git a/polygerrit-ui/app/elements/diff/gr-patch-range-select/gr-patch-range-select.ts b/polygerrit-ui/app/elements/diff/gr-patch-range-select/gr-patch-range-select.ts
index d9f88f7..325798c 100644
--- a/polygerrit-ui/app/elements/diff/gr-patch-range-select/gr-patch-range-select.ts
+++ b/polygerrit-ui/app/elements/diff/gr-patch-range-select/gr-patch-range-select.ts
@@ -21,6 +21,7 @@
 import {
   BasePatchSetNum,
   EDIT,
+  NumericChangeId,
   PARENT,
   PatchSetNum,
   RevisionInfo,
@@ -36,7 +37,7 @@
 import {EditRevisionInfo} from '../../../types/types';
 import {a11yStyles} from '../../../styles/gr-a11y-styles';
 import {sharedStyles} from '../../../styles/shared-styles';
-import {LitElement, PropertyValues, css, html} from 'lit';
+import {LitElement, css, html, nothing} from 'lit';
 import {customElement, property, query, state} from 'lit/decorators.js';
 import {subscribe} from '../../lit/subscription-controller';
 import {commentsModelToken} from '../../../models/comments/comments-model';
@@ -44,6 +45,8 @@
 import {ifDefined} from 'lit/directives/if-defined.js';
 import {ValueChangedEvent} from '../../../types/events';
 import {GeneratedWebLink} from '../../../utils/weblink-util';
+import {changeModelToken} from '../../../models/change/change-model';
+import {changeViewModelToken} from '../../../models/views/change';
 
 // Maximum length for patch set descriptions.
 const PATCH_DESC_MAX_LENGTH = 500;
@@ -83,33 +86,27 @@
   @query('#patchNumDropdown')
   patchNumDropdown?: GrDropdownList;
 
-  @property({type: Array})
-  availablePatches?: PatchSet[];
+  @state()
+  availablePatches: PatchSet[] = [];
 
-  @property({type: String})
-  changeNum?: string;
+  @state()
+  changeNum?: NumericChangeId;
 
   @property({type: Object})
   filesWeblinks?: FilesWebLinks;
 
-  @property({type: String})
+  @state()
   patchNum?: RevisionPatchSetNum;
 
-  @property({type: String})
+  @state()
   basePatchNum?: BasePatchSetNum;
 
-  /** Not used directly. Translated into `sortedRevisions` in willUpdate(). */
-  @property({type: Object})
-  revisions: (RevisionInfo | EditRevisionInfo)[] = [];
-
-  @property({type: Object})
+  @state()
   revisionInfo?: RevisionInfoClass;
 
-  /** Private internal state, derived from `revisions` in willUpdate(). */
   @state()
-  private sortedRevisions: (RevisionInfo | EditRevisionInfo)[] = [];
+  sortedRevisions: (RevisionInfo | EditRevisionInfo)[] = [];
 
-  /** Private internal state, visible for testing. */
   @state()
   changeComments?: ChangeComments;
 
@@ -118,10 +115,44 @@
 
   private readonly getCommentsModel = resolve(this, commentsModelToken);
 
+  private readonly getChangeModel = resolve(this, changeModelToken);
+
+  private readonly getViewModel = resolve(this, changeViewModelToken);
+
   constructor() {
     super();
     subscribe(
       this,
+      () => this.getViewModel().changeNum$,
+      x => (this.changeNum = x)
+    );
+    subscribe(
+      this,
+      () => this.getChangeModel().change$,
+      x => (this.revisionInfo = x ? new RevisionInfoClass(x) : undefined)
+    );
+    subscribe(
+      this,
+      () => this.getChangeModel().patchNum$,
+      x => (this.patchNum = x)
+    );
+    subscribe(
+      this,
+      () => this.getChangeModel().basePatchNum$,
+      x => (this.basePatchNum = x)
+    );
+    subscribe(
+      this,
+      () => this.getChangeModel().patchsets$,
+      x => (this.availablePatches = x)
+    );
+    subscribe(
+      this,
+      () => this.getChangeModel().revisions$,
+      x => (this.sortedRevisions = sortRevisions(Object.values(x || {})))
+    );
+    subscribe(
+      this,
       () => this.getCommentsModel().changeComments$,
       x => (this.changeComments = x)
     );
@@ -164,6 +195,9 @@
   }
 
   override render() {
+    if (!this.changeNum || !this.patchNum || !this.basePatchNum) {
+      return nothing;
+    }
     return html`
       <h3 class="assistive-tech-only">Patchset Range Selection</h3>
       <span class="patchRange" aria-label="patch range starts with">
@@ -203,16 +237,9 @@
     > `;
   }
 
-  override willUpdate(changedProperties: PropertyValues) {
-    if (changedProperties.has('revisions')) {
-      this.sortedRevisions = sortRevisions(Object.values(this.revisions || {}));
-    }
-  }
-
   // Private method, but visible for testing.
   computeBaseDropdownContent(): DropdownItem[] {
     if (
-      this.availablePatches === undefined ||
       this.patchNum === undefined ||
       this.changeComments === undefined ||
       this.revisionInfo === undefined
diff --git a/polygerrit-ui/app/elements/diff/gr-patch-range-select/gr-patch-range-select_test.ts b/polygerrit-ui/app/elements/diff/gr-patch-range-select/gr-patch-range-select_test.ts
index c90992f..584fcd7 100644
--- a/polygerrit-ui/app/elements/diff/gr-patch-range-select/gr-patch-range-select_test.ts
+++ b/polygerrit-ui/app/elements/diff/gr-patch-range-select/gr-patch-range-select_test.ts
@@ -9,7 +9,7 @@
 import {GrPatchRangeSelect} from './gr-patch-range-select';
 import {RevisionInfo as RevisionInfoClass} from '../../shared/revision-info/revision-info';
 import {ChangeComments} from '../gr-comment-api/gr-comment-api';
-import {stubReporting, stubRestApi} from '../../../test/test-utils';
+import {stubReporting} from '../../../test/test-utils';
 import {
   BasePatchSetNum,
   EDIT,
@@ -25,8 +25,11 @@
 import {EditRevisionInfo, ParsedChangeInfo} from '../../../types/types';
 import {SpecialFilePath} from '../../../constants/constants';
 import {
+  createChangeViewState,
   createEditRevision,
+  createParsedChange,
   createRevision,
+  createRevisions,
 } from '../../../test/test-data-generators';
 import {PatchSet} from '../../../utils/patch-set-util';
 import {
@@ -36,6 +39,9 @@
 import {queryAndAssert} from '../../../test/test-utils';
 import {fire} from '../../../utils/event-util';
 import {fixture, html, assert} from '@open-wc/testing';
+import {testResolver} from '../../../test/common-test-setup';
+import {changeViewModelToken} from '../../../models/views/change';
+import {changeModelToken} from '../../../models/change/change-model';
 
 type RevIdToRevisionInfo = {
   [revisionId: string]: RevisionInfo | EditRevisionInfo;
@@ -53,16 +59,23 @@
   }
 
   setup(async () => {
-    stubRestApi('getDiffComments').returns(Promise.resolve({}));
-    stubRestApi('getDiffRobotComments').returns(Promise.resolve({}));
-    stubRestApi('getDiffDrafts').returns(Promise.resolve({}));
-
     // Element must be wrapped in an element with direct access to the
     // comment API.
     element = await fixture(
       html`<gr-patch-range-select></gr-patch-range-select>`
     );
 
+    const viewModel = testResolver(changeViewModelToken);
+    viewModel.setState({
+      ...createChangeViewState(),
+      patchNum: 1 as RevisionPatchSetNum,
+      basePatchNum: PARENT,
+    });
+    const changeModel = testResolver(changeModelToken);
+    changeModel.updateStateChange({
+      ...createParsedChange(),
+      revisions: createRevisions(5),
+    });
     // Stub methods on the changeComments object after changeComments has
     // been initialized.
     element.changeComments = new ChangeComments();
@@ -86,7 +99,7 @@
   });
 
   test('enabled/disabled options', async () => {
-    element.revisions = [
+    element.sortedRevisions = [
       createRevision(3),
       createEditRevision(2),
       createRevision(2),
@@ -119,13 +132,13 @@
       {num: 2, sha: '3'} as PatchSet,
       {num: 1, sha: '4'} as PatchSet,
     ];
-    element.revisions = [
-      createRevision(2),
-      createRevision(3),
-      createRevision(1),
+    element.sortedRevisions = [
       createRevision(4),
+      createRevision(3),
+      createRevision(2),
+      createRevision(1),
     ];
-    element.revisionInfo = getInfo(element.revisions);
+    element.revisionInfo = getInfo(element.sortedRevisions);
     const expectedResult: DropdownItem[] = [
       {
         disabled: true,
@@ -175,13 +188,13 @@
   });
 
   test('computeBaseDropdownContent called when patchNum updates', async () => {
-    element.revisions = [
-      createRevision(2),
-      createRevision(3),
-      createRevision(1),
+    element.sortedRevisions = [
       createRevision(4),
+      createRevision(3),
+      createRevision(2),
+      createRevision(1),
     ];
-    element.revisionInfo = getInfo(element.revisions);
+    element.revisionInfo = getInfo(element.sortedRevisions);
     element.availablePatches = [
       {num: 1, sha: '1'} as PatchSet,
       {num: 2, sha: '2'} as PatchSet,
@@ -201,13 +214,13 @@
   });
 
   test('computeBaseDropdownContent called when changeComments update', async () => {
-    element.revisions = [
-      createRevision(2),
-      createRevision(3),
-      createRevision(1),
+    element.sortedRevisions = [
       createRevision(4),
+      createRevision(3),
+      createRevision(2),
+      createRevision(1),
     ];
-    element.revisionInfo = getInfo(element.revisions);
+    element.revisionInfo = getInfo(element.sortedRevisions);
     element.availablePatches = [
       {num: 3, sha: '2'} as PatchSet,
       {num: 2, sha: '3'} as PatchSet,
@@ -226,13 +239,13 @@
   });
 
   test('computePatchDropdownContent called when basePatchNum updates', async () => {
-    element.revisions = [
+    element.sortedRevisions = [
       createRevision(2),
       createRevision(3),
       createRevision(1),
       createRevision(4),
     ];
-    element.revisionInfo = getInfo(element.revisions);
+    element.revisionInfo = getInfo(element.sortedRevisions);
     element.availablePatches = [
       {num: 1, sha: '1'} as PatchSet,
       {num: 2, sha: '2'} as PatchSet,
@@ -258,7 +271,7 @@
       {num: 1, sha: '4'} as PatchSet,
     ];
     element.basePatchNum = 1 as BasePatchSetNum;
-    element.revisions = [
+    element.sortedRevisions = [
       createRevision(3),
       createEditRevision(2),
       createRevision(2, 'description'),
@@ -402,13 +415,13 @@
       {num: 2, sha: '3'} as PatchSet,
       {num: 1, sha: '4'} as PatchSet,
     ];
-    element.revisions = [
+    element.sortedRevisions = [
       createRevision(2),
       createRevision(3),
       createRevision(1),
       createRevision(4),
     ];
-    element.revisionInfo = getInfo(element.revisions);
+    element.revisionInfo = getInfo(element.sortedRevisions);
     await element.updateComplete;
 
     element.addEventListener('patch-range-change', handler);
@@ -444,13 +457,13 @@
       {num: 2, sha: '3'} as PatchSet,
       {num: 1, sha: '4'} as PatchSet,
     ];
-    element.revisions = [
+    element.sortedRevisions = [
       createRevision(2),
       createRevision(3),
       createRevision(1),
       createRevision(4),
     ];
-    element.revisionInfo = getInfo(element.revisions);
+    element.revisionInfo = getInfo(element.sortedRevisions);
     element.patchNum = 1 as PatchSetNumber;
     element.basePatchNum = PARENT;
     await element.updateComplete;
diff --git a/polygerrit-ui/app/elements/edit/gr-edit-controls/gr-edit-controls.ts b/polygerrit-ui/app/elements/edit/gr-edit-controls/gr-edit-controls.ts
index d1d05b7..ec1e48e 100644
--- a/polygerrit-ui/app/elements/edit/gr-edit-controls/gr-edit-controls.ts
+++ b/polygerrit-ui/app/elements/edit/gr-edit-controls/gr-edit-controls.ts
@@ -29,7 +29,7 @@
 import {customElement, property, query, state} from 'lit/decorators.js';
 import {BindValueChangeEvent} from '../../../types/events';
 import {IronInputElement} from '@polymer/iron-input/iron-input';
-import {createEditUrl} from '../../../models/views/edit';
+import {createEditUrl} from '../../../models/views/change';
 import {resolve} from '../../../models/dependency';
 import {modalStyles} from '../../../styles/gr-modal-styles';
 import {whenVisible} from '../../../utils/dom-util';
@@ -429,8 +429,8 @@
     const url = createEditUrl({
       changeNum: this.change._number,
       repo: this.change.project,
-      path: this.path,
       patchNum: this.patchNum,
+      editView: {path: this.path},
     });
 
     this.getNavigation().setUrl(url);
diff --git a/polygerrit-ui/app/elements/edit/gr-editor-view/gr-editor-view.ts b/polygerrit-ui/app/elements/edit/gr-editor-view/gr-editor-view.ts
index 8e346c3..acc4c9e 100644
--- a/polygerrit-ui/app/elements/edit/gr-editor-view/gr-editor-view.ts
+++ b/polygerrit-ui/app/elements/edit/gr-editor-view/gr-editor-view.ts
@@ -31,8 +31,12 @@
 import {resolve} from '../../../models/dependency';
 import {changeModelToken} from '../../../models/change/change-model';
 import {ShortcutController} from '../../lit/shortcut-controller';
-import {editViewModelToken, EditViewState} from '../../../models/views/edit';
-import {createChangeUrl} from '../../../models/views/change';
+import {
+  ChangeChildView,
+  changeViewModelToken,
+  ChangeViewState,
+  createChangeUrl,
+} from '../../../models/views/change';
 import {userModelToken} from '../../../models/user/user-model';
 import {storageServiceToken} from '../../../services/storage/gr-storage_impl';
 
@@ -60,7 +64,7 @@
    */
 
   @property({type: Object})
-  viewState?: EditViewState;
+  viewState?: ChangeViewState;
 
   // private but used in test
   @state() change?: ParsedChangeInfo;
@@ -95,7 +99,7 @@
 
   private readonly getChangeModel = resolve(this, changeModelToken);
 
-  private readonly getEditViewModel = resolve(this, editViewModelToken);
+  private readonly getViewModel = resolve(this, changeViewModelToken);
 
   private readonly getNavigation = resolve(this, navigationToken);
 
@@ -116,8 +120,10 @@
     );
     subscribe(
       this,
-      () => this.getEditViewModel().state$,
+      () => this.getViewModel().state$,
       state => {
+        // TODO: Add a setter for `viewState` instead of relying on the
+        // `viewStateChanged()` call here.
         this.viewState = state;
         this.viewStateChanged();
       }
@@ -206,7 +212,7 @@
   }
 
   override render() {
-    if (!this.viewState) return;
+    if (this.viewState?.childView !== ChangeChildView.EDIT) return nothing;
     return html` ${this.renderHeader()} ${this.renderEndpoint()} `;
   }
 
@@ -220,7 +226,7 @@
             <span class="separator"></span>
             <gr-editable-label
               labelText="File path"
-              .value=${this.viewState?.path}
+              .value=${this.viewState?.editView?.path}
               placeholder="File path..."
               @changed=${this.handlePathChanged}
             ></gr-editable-label>
@@ -277,7 +283,7 @@
           ></gr-endpoint-param>
           <gr-endpoint-param
             name="lineNum"
-            .value=${this.viewState?.lineNum}
+            .value=${this.viewState?.editView?.lineNum}
           ></gr-endpoint-param>
           <gr-default-editor
             id="file"
@@ -298,19 +304,21 @@
   }
 
   get storageKey() {
-    return `c${this.viewState?.changeNum}_ps${this.viewState?.patchNum}_${this.viewState?.path}`;
+    return `c${this.viewState?.changeNum}_ps${this.viewState?.patchNum}_${this.viewState?.editView?.path}`;
   }
 
   // private but used in test
   viewStateChanged() {
-    if (!this.viewState) return;
+    if (this.viewState?.childView !== ChangeChildView.EDIT) return;
 
     // NOTE: This may be called before attachment (e.g. while parentElement is
     // null). Fire title-change in an async so that, if attachment to the DOM
     // has been queued, the event can bubble up to the handler in gr-app.
     setTimeout(() => {
       if (!this.viewState) return;
-      const title = `Editing ${computeTruncatedPath(this.viewState.path)}`;
+      const title = `Editing ${computeTruncatedPath(
+        this.viewState.editView?.path
+      )}`;
       fireTitleChange(this, title);
     });
 
@@ -347,7 +355,7 @@
   // private but used in test
   async handlePathChanged(e: CustomEvent<string>): Promise<void> {
     const changeNum = this.viewState?.changeNum;
-    const currentPath = this.viewState?.path;
+    const currentPath = this.viewState?.editView?.path;
     assertIsDefined(changeNum, 'change number');
     assertIsDefined(currentPath, 'path');
 
@@ -376,7 +384,7 @@
   getFileData() {
     const changeNum = this.viewState?.changeNum;
     const patchNum = this.viewState?.patchNum;
-    const path = this.viewState?.path;
+    const path = this.viewState?.editView?.path;
     assertIsDefined(changeNum, 'change number');
     assertIsDefined(patchNum, 'patchset number');
     assertIsDefined(path, 'path');
@@ -416,7 +424,7 @@
   // private but used in test
   saveEdit() {
     const changeNum = this.viewState?.changeNum;
-    const path = this.viewState?.path;
+    const path = this.viewState?.editView?.path;
     assertIsDefined(changeNum, 'change number');
     assertIsDefined(path, 'path');
 
diff --git a/polygerrit-ui/app/elements/edit/gr-editor-view/gr-editor-view_test.ts b/polygerrit-ui/app/elements/edit/gr-editor-view/gr-editor-view_test.ts
index d428e18..1a4879d 100644
--- a/polygerrit-ui/app/elements/edit/gr-editor-view/gr-editor-view_test.ts
+++ b/polygerrit-ui/app/elements/edit/gr-editor-view/gr-editor-view_test.ts
@@ -72,7 +72,7 @@
                 labeltext="File path"
                 placeholder="File path..."
                 tabindex="0"
-                title="${element.viewState?.path}"
+                title="${element.viewState?.editView?.path}"
               >
               </gr-editable-label>
             </span>
@@ -373,7 +373,7 @@
         ...createEditViewState(),
         changeNum: 1 as NumericChangeId,
         patchNum: EDIT,
-        path: 'test/path',
+        editView: {path: 'test/path'},
       };
 
       // Ensure no data is set with a bad response.
@@ -392,7 +392,7 @@
         ...createEditViewState(),
         changeNum: 1 as NumericChangeId,
         patchNum: EDIT,
-        path: 'test/path',
+        editView: {path: 'test/path'},
       };
 
       // Ensure no data is set with a bad response.
@@ -415,7 +415,7 @@
         ...createEditViewState(),
         changeNum: 1 as NumericChangeId,
         patchNum: EDIT,
-        path: 'test/path',
+        editView: {path: 'test/path'},
       };
 
       return element.getFileData().then(() => {
@@ -433,7 +433,7 @@
         ...createEditViewState(),
         changeNum: 1 as NumericChangeId,
         patchNum: EDIT,
-        path: 'test/path',
+        editView: {path: 'test/path'},
       };
 
       return element.getFileData().then(() => {
@@ -530,7 +530,7 @@
         ...createEditViewState(),
         changeNum: 1 as NumericChangeId,
         patchNum: 1 as RevisionPatchSetNum,
-        path: 'test',
+        editView: {path: 'test'},
       };
 
       const alertStub = sinon.stub();
@@ -562,7 +562,7 @@
         ...createEditViewState(),
         changeNum: 1 as NumericChangeId,
         patchNum: 1 as RevisionPatchSetNum,
-        path: 'test',
+        editView: {path: 'test'},
       };
 
       const alertStub = sinon.stub();
@@ -583,7 +583,7 @@
         ...createEditViewState(),
         changeNum: 1 as NumericChangeId,
         patchNum: 1 as RevisionPatchSetNum,
-        path: 'test',
+        editView: {path: 'test'},
       };
       assert.equal(element.storageKey, 'c1_ps1_test');
     });
diff --git a/polygerrit-ui/app/elements/gr-app-element.ts b/polygerrit-ui/app/elements/gr-app-element.ts
index e959e05..eceb05e 100644
--- a/polygerrit-ui/app/elements/gr-app-element.ts
+++ b/polygerrit-ui/app/elements/gr-app-element.ts
@@ -74,6 +74,7 @@
 import {userModelToken} from '../models/user/user-model';
 import {modalStyles} from '../styles/gr-modal-styles';
 import {AdminChildView, createAdminUrl} from '../models/views/admin';
+import {ChangeChildView, changeViewModelToken} from '../models/views/change';
 
 interface ErrorInfo {
   text: string;
@@ -119,6 +120,9 @@
 
   @state() private view?: GerritView;
 
+  // TODO: Introduce a wrapper element for CHANGE, DIFF, EDIT view.
+  @state() private childView?: ChangeChildView;
+
   @state() private lastError?: ErrorInfo;
 
   // private but used in test
@@ -168,6 +172,8 @@
 
   private readonly getRouterModel = resolve(this, routerModelToken);
 
+  private readonly getChangeViewModel = resolve(this, changeViewModelToken);
+
   constructor() {
     super();
 
@@ -237,6 +243,13 @@
         if (view) this.errorView?.classList.remove('show');
       }
     );
+    subscribe(
+      this,
+      () => this.getChangeViewModel().childView$,
+      childView => {
+        this.childView = childView;
+      }
+    );
 
     prefersDarkColorScheme().addEventListener('change', () => {
       if (this.theme === AppTheme.AUTO) {
@@ -464,9 +477,7 @@
       this.updateComplete.then(() => (this.invalidateChangeViewCache = false));
       return nothing;
     }
-    return cache(
-      this.view === GerritView.CHANGE ? this.changeViewTemplate() : nothing
-    );
+    return cache(this.isChangeView() ? this.changeViewTemplate() : nothing);
   }
 
   // Template as not to create duplicates, for renderChangeView() only.
@@ -476,8 +487,27 @@
     `;
   }
 
+  private isChangeView() {
+    return (
+      this.view === GerritView.CHANGE &&
+      this.childView === ChangeChildView.OVERVIEW
+    );
+  }
+
+  private isDiffView() {
+    return (
+      this.view === GerritView.CHANGE && this.childView === ChangeChildView.DIFF
+    );
+  }
+
+  private isEditorView() {
+    return (
+      this.view === GerritView.CHANGE && this.childView === ChangeChildView.EDIT
+    );
+  }
+
   private renderEditorView() {
-    if (this.view !== GerritView.EDIT) return nothing;
+    if (!this.isEditorView()) return nothing;
     return html`<gr-editor-view></gr-editor-view>`;
   }
 
@@ -486,9 +516,7 @@
       this.updateComplete.then(() => (this.invalidateDiffViewCache = false));
       return nothing;
     }
-    return cache(
-      this.view === GerritView.DIFF ? this.diffViewTemplate() : nothing
-    );
+    return cache(this.isDiffView() ? this.diffViewTemplate() : nothing);
   }
 
   private diffViewTemplate() {
diff --git a/polygerrit-ui/app/elements/gr-app-types.ts b/polygerrit-ui/app/elements/gr-app-types.ts
index 3008236..0261992 100644
--- a/polygerrit-ui/app/elements/gr-app-types.ts
+++ b/polygerrit-ui/app/elements/gr-app-types.ts
@@ -13,8 +13,6 @@
 import {SearchViewState} from '../models/views/search';
 import {DashboardViewState} from '../models/views/dashboard';
 import {ChangeViewState} from '../models/views/change';
-import {DiffViewState} from '../models/views/diff';
-import {EditViewState} from '../models/views/edit';
 
 export interface AppElement extends HTMLElement {
   params: AppElementParams;
@@ -41,8 +39,6 @@
   | SearchViewState
   | SettingsViewState
   | AgreementViewState
-  | DiffViewState
-  | EditViewState
   | AppElementJustRegisteredParams;
 
 export function isAppElementJustRegisteredParams(
diff --git a/polygerrit-ui/app/elements/shared/gr-comment-thread/gr-comment-thread.ts b/polygerrit-ui/app/elements/shared/gr-comment-thread/gr-comment-thread.ts
index df41b1f4..dd0fbca 100644
--- a/polygerrit-ui/app/elements/shared/gr-comment-thread/gr-comment-thread.ts
+++ b/polygerrit-ui/app/elements/shared/gr-comment-thread/gr-comment-thread.ts
@@ -72,8 +72,7 @@
 import {whenRendered} from '../../../utils/dom-util';
 import {Interaction} from '../../../constants/reporting';
 import {HtmlPatched} from '../../../utils/lit-util';
-import {createDiffUrl} from '../../../models/views/diff';
-import {createChangeUrl} from '../../../models/views/change';
+import {createChangeUrl, createDiffUrl} from '../../../models/views/change';
 import {userModelToken} from '../../../models/user/user-model';
 import {highlightServiceToken} from '../../../services/highlight/highlight-service';
 
@@ -746,8 +745,8 @@
     return createDiffUrl({
       changeNum: this.changeNum,
       repo: this.repoName,
-      path: this.thread.path,
       patchNum: this.thread.patchNum,
+      diffView: {path: this.thread.path},
     });
   }
 
diff --git a/polygerrit-ui/app/elements/shared/gr-comment/gr-comment.ts b/polygerrit-ui/app/elements/shared/gr-comment/gr-comment.ts
index 090dfef..66beaf1 100644
--- a/polygerrit-ui/app/elements/shared/gr-comment/gr-comment.ts
+++ b/polygerrit-ui/app/elements/shared/gr-comment/gr-comment.ts
@@ -60,7 +60,7 @@
 import {Interaction} from '../../../constants/reporting';
 import {KnownExperimentId} from '../../../services/flags/flags';
 import {isBase64FileContent} from '../../../api/rest-api';
-import {createDiffUrl} from '../../../models/views/diff';
+import {createDiffUrl} from '../../../models/views/change';
 import {userModelToken} from '../../../models/user/user-model';
 import {modalStyles} from '../../../styles/gr-modal-styles';
 
@@ -547,8 +547,9 @@
           ${this.renderDraftLabel()}
         </div>
         <div class="headerMiddle">${this.renderCollapsedContent()}</div>
-        ${this.renderRunDetails()} ${this.renderDeleteButton()}
-        ${this.renderPatchset()} ${this.renderDate()} ${this.renderToggle()}
+        ${this.renderSuggestEditButton()} ${this.renderRunDetails()}
+        ${this.renderDeleteButton()} ${this.renderPatchset()}
+        ${this.renderDate()} ${this.renderToggle()}
       </div>
     `;
   }
@@ -777,10 +778,9 @@
     return html`
       <div class="rightActions">
         ${this.autoSaving ? html`.&nbsp;&nbsp;` : ''}
-        ${this.renderDiscardButton()} ${this.renderSuggestEditButton()}
-        ${this.renderPreviewSuggestEditButton()} ${this.renderEditButton()}
-        ${this.renderCancelButton()} ${this.renderSaveButton()}
-        ${this.renderCopyLinkIcon()}
+        ${this.renderDiscardButton()} ${this.renderPreviewSuggestEditButton()}
+        ${this.renderEditButton()} ${this.renderCancelButton()}
+        ${this.renderSaveButton()} ${this.renderCopyLinkIcon()}
       </div>
     `;
   }
@@ -809,6 +809,7 @@
       return nothing;
     }
     if (
+      !this.editing ||
       this.permanentEditingMode ||
       this.comment?.path === SpecialFilePath.PATCHSET_LEVEL_COMMENTS
     ) {
@@ -1139,7 +1140,8 @@
     fire(this, 'open-fix-preview', await this.createFixPreview());
   }
 
-  async createSuggestEdit() {
+  async createSuggestEdit(e: MouseEvent) {
+    e.stopPropagation();
     const line = await this.getCommentedCode();
     this.messageText += `${USER_SUGGESTION_START_PATTERN}${line}${'\n```'}`;
   }
diff --git a/polygerrit-ui/app/elements/shared/gr-comment/gr-comment_test.ts b/polygerrit-ui/app/elements/shared/gr-comment/gr-comment_test.ts
index ec9c875..3390369 100644
--- a/polygerrit-ui/app/elements/shared/gr-comment/gr-comment_test.ts
+++ b/polygerrit-ui/app/elements/shared/gr-comment/gr-comment_test.ts
@@ -854,12 +854,12 @@
           .initiallyCollapsed=${false}
         ></gr-comment>`
       );
+      element.editing = true;
     });
     test('renders suggest fix button', () => {
       assert.dom.equal(
         queryAndAssert(element, 'gr-button.suggestEdit'),
         /* HTML */ `<gr-button
-          aria-disabled="false"
           class="action suggestEdit"
           link=""
           role="button"
diff --git a/polygerrit-ui/app/elements/shared/gr-textarea/gr-textarea_test.ts b/polygerrit-ui/app/elements/shared/gr-textarea/gr-textarea_test.ts
index 1460246..f8ae38c 100644
--- a/polygerrit-ui/app/elements/shared/gr-textarea/gr-textarea_test.ts
+++ b/polygerrit-ui/app/elements/shared/gr-textarea/gr-textarea_test.ts
@@ -553,7 +553,7 @@
     assert.deepEqual(indentCommand.args[0], ['insertText', false, '\n    ']);
   });
 
-  test('emoji dropdown is closed when iron-overlay-closed is fired', async () => {
+  test('emoji dropdown is closed when dropdown-closed is fired', async () => {
     const resetSpy = sinon.spy(element, 'closeDropdown');
     element.emojiSuggestions!.dispatchEvent(
       new CustomEvent('dropdown-closed', {
diff --git a/polygerrit-ui/app/embed/diff/gr-diff/gr-diff-utils.ts b/polygerrit-ui/app/embed/diff/gr-diff/gr-diff-utils.ts
index 3392951..87fd5ca 100644
--- a/polygerrit-ui/app/embed/diff/gr-diff/gr-diff-utils.ts
+++ b/polygerrit-ui/app/embed/diff/gr-diff/gr-diff-utils.ts
@@ -48,6 +48,12 @@
   }, 0);
 }
 
+export function isFileUnchanged(diff: DiffInfo) {
+  return !diff.content.some(
+    content => (content.a && !content.common) || (content.b && !content.common)
+  );
+}
+
 export function getResponsiveMode(
   prefs?: DiffPreferencesInfo,
   renderPrefs?: RenderPreferences
diff --git a/polygerrit-ui/app/embed/diff/gr-diff/gr-diff-utils_test.ts b/polygerrit-ui/app/embed/diff/gr-diff/gr-diff-utils_test.ts
index 98b4586..25dc768 100644
--- a/polygerrit-ui/app/embed/diff/gr-diff/gr-diff-utils_test.ts
+++ b/polygerrit-ui/app/embed/diff/gr-diff/gr-diff-utils_test.ts
@@ -4,8 +4,15 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 import {assert} from '@open-wc/testing';
+import {DiffInfo} from '../../../api/diff';
 import '../../../test/common-test-setup';
-import {createElementDiff, formatText, createTabWrapper} from './gr-diff-utils';
+import {createDiff} from '../../../test/test-data-generators';
+import {
+  createElementDiff,
+  formatText,
+  createTabWrapper,
+  isFileUnchanged,
+} from './gr-diff-utils';
 
 const LINE_BREAK_HTML = '<span class="gr-diff br"></span>';
 
@@ -156,4 +163,36 @@
     expectTextLength('abc\tde\t', 10, 20);
     expectTextLength('\t\t\t\t\t', 20, 100);
   });
+
+  test('isFileUnchanged', () => {
+    let diff: DiffInfo = {
+      ...createDiff(),
+      content: [
+        {a: ['abcd'], ab: ['ef']},
+        {b: ['ancd'], a: ['xx']},
+      ],
+    };
+    assert.equal(isFileUnchanged(diff), false);
+    diff = {
+      ...createDiff(),
+      content: [{ab: ['abcd']}, {ab: ['ancd']}],
+    };
+    assert.equal(isFileUnchanged(diff), true);
+    diff = {
+      ...createDiff(),
+      content: [
+        {a: ['abcd'], ab: ['ef'], common: true},
+        {b: ['ancd'], ab: ['xx']},
+      ],
+    };
+    assert.equal(isFileUnchanged(diff), false);
+    diff = {
+      ...createDiff(),
+      content: [
+        {a: ['abcd'], ab: ['ef'], common: true},
+        {b: ['ancd'], ab: ['xx'], common: true},
+      ],
+    };
+    assert.equal(isFileUnchanged(diff), true);
+  });
 });
diff --git a/polygerrit-ui/app/embed/diff/gr-diff/gr-diff.ts b/polygerrit-ui/app/embed/diff/gr-diff/gr-diff.ts
index 2097170..a0526ed 100644
--- a/polygerrit-ui/app/embed/diff/gr-diff/gr-diff.ts
+++ b/polygerrit-ui/app/embed/diff/gr-diff/gr-diff.ts
@@ -755,9 +755,9 @@
           rule wins in case of same specificity.
         */
         .trailing-whitespace,
-        .content .trailing-whitespace,
+        .content .contentText .trailing-whitespace,
         .trailing-whitespace .intraline,
-        .content .trailing-whitespace .intraline {
+        .content .contentText .trailing-whitespace .intraline {
           border-radius: var(--border-radius, 4px);
           background-color: var(--diff-trailing-whitespace-indicator);
         }
diff --git a/polygerrit-ui/app/models/change/change-model.ts b/polygerrit-ui/app/models/change/change-model.ts
index 8282a3f..446822f 100644
--- a/polygerrit-ui/app/models/change/change-model.ts
+++ b/polygerrit-ui/app/models/change/change-model.ts
@@ -12,6 +12,7 @@
   PatchSetNum,
   PreferencesInfo,
   RevisionPatchSetNum,
+  PatchSetNumber,
 } from '../../types/common';
 import {DefaultBase} from '../../constants/constants';
 import {combineLatest, from, fromEvent, Observable, forkJoin, of} from 'rxjs';
@@ -22,7 +23,6 @@
   startWith,
   switchMap,
 } from 'rxjs/operators';
-import {RouterModel} from '../../services/router/router-model';
 import {
   computeAllPatchSets,
   computeLatestPatchNum,
@@ -38,6 +38,13 @@
 import {UserModel} from '../user/user-model';
 import {define} from '../dependency';
 import {isOwner} from '../../utils/change-util';
+import {
+  ChangeViewModel,
+  createChangeUrl,
+  createDiffUrl,
+  createEditUrl,
+} from '../views/change';
+import {NavigationService} from '../../elements/core/gr-navigation/gr-navigation';
 
 export enum LoadingStatus {
   NOT_LOADED = 'NOT_LOADED',
@@ -56,12 +63,6 @@
   loadingStatus: LoadingStatus;
   change?: ParsedChangeInfo;
   /**
-   * The name of the file user is viewing in the diff view mode. File path is
-   * specified in the url or derived from the commentId.
-   * Does not apply to change-view or edit-view.
-   */
-  diffPath?: string;
-  /**
    * The list of reviewed files, kept in the model because we want changes made
    * in one view to reflect on other views without re-rendering the other views.
    * Undefined means it's still loading and empty set means no files reviewed.
@@ -76,7 +77,7 @@
 export function updateChangeWithEdit(
   change?: ParsedChangeInfo,
   edit?: EditInfo,
-  routerPatchNum?: PatchSetNum
+  viewModelPatchNum?: PatchSetNum
 ): ParsedChangeInfo | undefined {
   if (!change || !edit) return change;
   assertIsDefined(edit.commit.commit, 'edit.commit.commit');
@@ -95,7 +96,7 @@
   // which is still done in change-view. `_patchRange.patchNum` should
   // eventually also be model managed, so we can reconcile these two code
   // snippets into one location.
-  if (routerPatchNum === undefined) {
+  if (viewModelPatchNum === undefined) {
     change.current_revision = edit.commit.commit;
   }
   return change;
@@ -103,20 +104,20 @@
 
 /**
  * Derives the base patchset number from all the data that can potentially
- * influence it. Mostly just returns `routerBasePatchNum` or PARENT, but has
+ * influence it. Mostly just returns `viewModelBasePatchNum` or PARENT, but has
  * some special logic when looking at merge commits.
  *
- * NOTE: At the moment this returns just `routerBasePatchNum ?? PARENT`, see
+ * NOTE: At the moment this returns just `viewModelBasePatchNum ?? PARENT`, see
  * TODO below.
  */
 function computeBase(
-  routerBasePatchNum: BasePatchSetNum | undefined,
+  viewModelBasePatchNum: BasePatchSetNum | undefined,
   patchNum: RevisionPatchSetNum | undefined,
   change: ParsedChangeInfo | undefined,
   preferences: PreferencesInfo
 ): BasePatchSetNum {
-  if (routerBasePatchNum && routerBasePatchNum !== PARENT) {
-    return routerBasePatchNum;
+  if (viewModelBasePatchNum && viewModelBasePatchNum !== PARENT) {
+    return viewModelBasePatchNum;
   }
   if (!change || !patchNum) return PARENT;
 
@@ -129,7 +130,7 @@
   // but we are not sure whether this was ever 100% working correctly. A
   // major challenge is being able to select PARENT explicitly even if your
   // preference for the default choice is FIRST_PARENT. <gr-file-list-header>
-  // just uses `navigation.setUrl()` and the router does not have any
+  // just uses `navigation.setUrl()` and the view model does not have any
   // way of forcing the basePatchSetNum to stick to PARENT without being
   // altered back to FIRST_PARENT here.
   // See also corresponding TODO in gr-settings-view.
@@ -150,7 +151,11 @@
 export class ChangeModel extends Model<ChangeState> {
   private change?: ParsedChangeInfo;
 
-  private patchNum?: PatchSetNum;
+  private patchNum?: RevisionPatchSetNum;
+
+  private basePatchNum?: BasePatchSetNum;
+
+  private latestPatchNum?: PatchSetNumber;
 
   public readonly change$ = select(
     this.state$,
@@ -162,11 +167,6 @@
     changeState => changeState.loadingStatus
   );
 
-  public readonly diffPath$ = select(
-    this.state$,
-    changeState => changeState?.diffPath
-  );
-
   public readonly reviewedFiles$ = select(
     this.state$,
     changeState => changeState?.reviewedFiles
@@ -178,8 +178,17 @@
 
   public readonly labels$ = select(this.change$, change => change?.labels);
 
-  public readonly latestPatchNum$ = select(this.change$, change =>
-    computeLatestPatchNum(computeAllPatchSets(change))
+  public readonly revisions$ = select(
+    this.change$,
+    change => change?.revisions
+  );
+
+  public readonly patchsets$ = select(this.change$, change =>
+    computeAllPatchSets(change)
+  );
+
+  public readonly latestPatchNum$ = select(this.patchsets$, patchsets =>
+    computeLatestPatchNum(patchsets)
   );
 
   /**
@@ -192,57 +201,57 @@
   public readonly patchNum$: Observable<RevisionPatchSetNum | undefined> =
     select(
       combineLatest([
-        this.routerModel.state$,
+        this.viewModel.state$,
         this.state$,
         this.latestPatchNum$,
       ]).pipe(
         /**
-         * If you depend on both, router and change state, then you want to
-         * filter out inconsistent state, e.g. router changeNum already updated,
-         * change not yet reset to undefined.
+         * If you depend on both, view model and change state, then you want to
+         * filter out inconsistent state, e.g. view model changeNum already
+         * updated, change not yet reset to undefined.
          */
-        filter(([routerState, changeState, _latestPatchN]) => {
+        filter(([viewModelState, changeState, _latestPatchN]) => {
           const changeNum = changeState.change?._number;
-          const routerChangeNum = routerState.changeNum;
-          return changeNum === undefined || changeNum === routerChangeNum;
+          const viewModelChangeNum = viewModelState?.changeNum;
+          return changeNum === undefined || changeNum === viewModelChangeNum;
         })
       ),
-      ([routerState, _changeState, latestPatchN]) =>
-        routerState?.patchNum || latestPatchN
+      ([viewModelState, _changeState, latestPatchN]) =>
+        viewModelState?.patchNum || latestPatchN
     );
 
   /**
    * Emits the base patchset number. This is identical to the
-   * `routerBasePatchNum$`, but has some special logic for merges.
+   * `viewModel.basePatchNum$`, but has some special logic for merges.
    *
    * Note that this selector can emit without the change being available!
    */
   public readonly basePatchNum$: Observable<BasePatchSetNum> =
     /**
-     * If you depend on both, router and change state, then you want to filter
-     * out inconsistent state, e.g. router changeNum already updated, change not
-     * yet reset to undefined.
+     * If you depend on both, view model and change state, then you want to
+     * filter out inconsistent state, e.g. view model changeNum already
+     * updated, change not yet reset to undefined.
      */
     select(
       combineLatest([
-        this.routerModel.state$,
+        this.viewModel.state$,
         this.state$,
         this.userModel.state$,
       ]).pipe(
-        filter(([routerState, changeState, _]) => {
+        filter(([viewModelState, changeState, _]) => {
           const changeNum = changeState.change?._number;
-          const routerChangeNum = routerState.changeNum;
-          return changeNum === undefined || changeNum === routerChangeNum;
+          const viewModelChangeNum = viewModelState?.changeNum;
+          return changeNum === undefined || changeNum === viewModelChangeNum;
         }),
         withLatestFrom(
-          this.routerModel.routerBasePatchNum$,
+          this.viewModel.basePatchNum$,
           this.patchNum$,
           this.change$,
           this.userModel.preferences$
         )
       ),
-      ([_, routerBasePatchNum, patchNum, change, preferences]) =>
-        computeBase(routerBasePatchNum, patchNum, change, preferences)
+      ([_, viewModelBasePatchNum, patchNum, change, preferences]) =>
+        computeBase(viewModelBasePatchNum, patchNum, change, preferences)
     );
 
   public readonly isOwner$: Observable<boolean> = select(
@@ -257,13 +266,14 @@
   );
 
   constructor(
-    private readonly routerModel: RouterModel,
+    private readonly navigation: NavigationService,
+    private readonly viewModel: ChangeViewModel,
     private readonly restApiService: RestApiService,
     private readonly userModel: UserModel
   ) {
     super(initialState);
     this.subscriptions = [
-      combineLatest([this.routerModel.routerChangeNum$, this.reload$])
+      combineLatest([this.viewModel.changeNum$, this.reload$])
         .pipe(
           map(([changeNum, _]) => changeNum),
           switchMap(changeNum => {
@@ -272,7 +282,7 @@
             const edit = from(this.restApiService.getChangeEdit(changeNum));
             return forkJoin([change, edit]);
           }),
-          withLatestFrom(this.routerModel.routerPatchNum$),
+          withLatestFrom(this.viewModel.patchNum$),
           map(([[change, edit], patchNum]) =>
             updateChangeWithEdit(change, edit, patchNum)
           )
@@ -289,6 +299,12 @@
         }),
       this.change$.subscribe(change => (this.change = change)),
       this.patchNum$.subscribe(patchNum => (this.patchNum = patchNum)),
+      this.basePatchNum$.subscribe(
+        basePatchNum => (this.basePatchNum = basePatchNum)
+      ),
+      this.latestPatchNum$.subscribe(
+        latestPatchNum => (this.latestPatchNum = latestPatchNum)
+      ),
       combineLatest([this.patchNum$, this.changeNum$, this.userModel.loggedIn$])
         .pipe(
           switchMap(([patchNum, changeNum, loggedIn]) => {
@@ -303,11 +319,6 @@
     ];
   }
 
-  // Temporary workaround until path is derived in the model itself.
-  updatePath(diffPath?: string) {
-    this.updateState({diffPath});
-  }
-
   updateStateReviewedFiles(reviewedFiles: string[]) {
     this.updateState({reviewedFiles});
   }
@@ -372,6 +383,65 @@
     return this.getState().change;
   }
 
+  diffUrl(
+    diffView: {path: string; lineNum?: number},
+    patchNum = this.patchNum,
+    basePatchNum = this.basePatchNum
+  ) {
+    if (!this.change) return;
+    if (!this.patchNum) return;
+    return createDiffUrl({
+      change: this.change,
+      patchNum,
+      basePatchNum,
+      diffView,
+    });
+  }
+
+  navigateToDiff(
+    diffView: {path: string; lineNum?: number},
+    patchNum = this.patchNum,
+    basePatchNum = this.basePatchNum
+  ) {
+    const url = this.diffUrl(diffView, patchNum, basePatchNum);
+    if (!url) return;
+    this.navigation.setUrl(url);
+  }
+
+  changeUrl(openReplyDialog = false) {
+    if (!this.change) return;
+    const isLatest = this.latestPatchNum === this.patchNum;
+    return createChangeUrl({
+      change: this.change,
+      patchNum:
+        isLatest && this.basePatchNum === PARENT ? undefined : this.patchNum,
+      basePatchNum: this.basePatchNum,
+      openReplyDialog,
+    });
+  }
+
+  navigateToChange(openReplyDialog = false) {
+    const url = this.changeUrl(openReplyDialog);
+    if (!url) return;
+    this.navigation.setUrl(url);
+  }
+
+  editUrl(editView: {path: string; lineNum?: number}) {
+    if (!this.change) return;
+    return createEditUrl({
+      changeNum: this.change._number,
+      repo: this.change.project,
+      patchNum: this.patchNum,
+      editView,
+    });
+  }
+
+  navigateToEdit(editView: {path: string; lineNum?: number}) {
+    const url = this.editUrl(editView);
+    if (!url) return;
+    this.navigation.setUrl(url);
+  }
+
   /**
    * Check whether there is no newer patch than the latest patch that was
    * available when this change was loaded.
diff --git a/polygerrit-ui/app/models/change/change-model_test.ts b/polygerrit-ui/app/models/change/change-model_test.ts
index a2fc7c9..c11c15b 100644
--- a/polygerrit-ui/app/models/change/change-model_test.ts
+++ b/polygerrit-ui/app/models/change/change-model_test.ts
@@ -9,6 +9,7 @@
 import {
   createChange,
   createChangeMessageInfo,
+  createChangeViewState,
   createEditInfo,
   createParsedChange,
   createRevision,
@@ -28,12 +29,13 @@
 } from '../../types/common';
 import {ParsedChangeInfo} from '../../types/types';
 import {getAppContext} from '../../services/app-context';
-import {GerritView, routerModelToken} from '../../services/router/router-model';
 import {ChangeState, LoadingStatus, updateChangeWithEdit} from './change-model';
 import {ChangeModel} from './change-model';
 import {assert} from '@open-wc/testing';
 import {testResolver} from '../../test/common-test-setup';
 import {userModelToken} from '../user/user-model';
+import {changeViewModelToken} from '../views/change';
+import {navigationToken} from '../../elements/core/gr-navigation/gr-navigation';
 
 suite('updateChangeWithEdit() tests', () => {
   test('undefined change', async () => {
@@ -83,7 +85,8 @@
 
   setup(() => {
     changeModel = new ChangeModel(
-      testResolver(routerModelToken),
+      testResolver(navigationToken),
+      testResolver(changeViewModelToken),
       getAppContext().restApiService,
       testResolver(userModelToken)
     );
@@ -121,10 +124,7 @@
     assert.equal(stub.callCount, 0);
     assert.isUndefined(state?.change);
 
-    testResolver(routerModelToken).setState({
-      view: GerritView.CHANGE,
-      changeNum: knownChange._number,
-    });
+    testResolver(changeViewModelToken).setState(createChangeViewState());
     state = await waitForLoadingStatus(LoadingStatus.LOADING);
     assert.equal(stub.callCount, 1);
     assert.isUndefined(state?.change);
@@ -140,10 +140,7 @@
     const promise = mockPromise<ParsedChangeInfo | undefined>();
     const stub = stubRestApi('getChangeDetail').callsFake(() => promise);
     let state: ChangeState;
-    testResolver(routerModelToken).setState({
-      view: GerritView.CHANGE,
-      changeNum: knownChange._number,
-    });
+    testResolver(changeViewModelToken).setState(createChangeViewState());
     promise.resolve(knownChange);
     state = await waitForLoadingStatus(LoadingStatus.LOADED);
 
@@ -164,10 +161,7 @@
     let promise = mockPromise<ParsedChangeInfo | undefined>();
     const stub = stubRestApi('getChangeDetail').callsFake(() => promise);
     let state: ChangeState;
-    testResolver(routerModelToken).setState({
-      view: GerritView.CHANGE,
-      changeNum: knownChange._number,
-    });
+    testResolver(changeViewModelToken).setState(createChangeViewState());
     promise.resolve(knownChange);
     state = await waitForLoadingStatus(LoadingStatus.LOADED);
 
@@ -178,8 +172,8 @@
       _number: 123 as NumericChangeId,
     };
     promise = mockPromise<ParsedChangeInfo | undefined>();
-    testResolver(routerModelToken).setState({
-      view: GerritView.CHANGE,
+    testResolver(changeViewModelToken).setState({
+      ...createChangeViewState(),
       changeNum: otherChange._number,
     });
     state = await waitForLoadingStatus(LoadingStatus.LOADING);
@@ -197,10 +191,7 @@
     let promise = mockPromise<ParsedChangeInfo | undefined>();
     const stub = stubRestApi('getChangeDetail').callsFake(() => promise);
     let state: ChangeState;
-    testResolver(routerModelToken).setState({
-      view: GerritView.CHANGE,
-      changeNum: knownChange._number,
-    });
+    testResolver(changeViewModelToken).setState(createChangeViewState());
     promise.resolve(knownChange);
     state = await waitForLoadingStatus(LoadingStatus.LOADED);
 
@@ -208,10 +199,7 @@
 
     promise = mockPromise<ParsedChangeInfo | undefined>();
     promise.resolve(undefined);
-    testResolver(routerModelToken).setState({
-      view: GerritView.CHANGE,
-      changeNum: undefined,
-    });
+    testResolver(changeViewModelToken).setState(undefined);
     state = await waitForLoadingStatus(LoadingStatus.NOT_LOADED);
     assert.equal(stub.callCount, 2);
     assert.isUndefined(state?.change);
@@ -220,10 +208,7 @@
 
     promise = mockPromise<ParsedChangeInfo | undefined>();
     promise.resolve(knownChange);
-    testResolver(routerModelToken).setState({
-      view: GerritView.CHANGE,
-      changeNum: knownChange._number,
-    });
+    testResolver(changeViewModelToken).setState(createChangeViewState());
     state = await waitForLoadingStatus(LoadingStatus.LOADED);
     assert.equal(stub.callCount, 3);
     assert.equal(state?.change, knownChange);
@@ -299,7 +284,7 @@
     assert.equal(spy.lastCall.firstArg, PARENT);
 
     // test update
-    testResolver(routerModelToken).updateState({
+    testResolver(changeViewModelToken).updateState({
       basePatchNum: 1 as PatchSetNumber,
     });
     assert.equal(spy.callCount, 2);
diff --git a/polygerrit-ui/app/models/change/files-model.ts b/polygerrit-ui/app/models/change/files-model.ts
index 07e64a2..0683af0 100644
--- a/polygerrit-ui/app/models/change/files-model.ts
+++ b/polygerrit-ui/app/models/change/files-model.ts
@@ -23,6 +23,9 @@
 import {ChangeModel} from './change-model';
 import {CommentsModel} from '../comments/comments-model';
 
+export type FileNameToNormalizedFileInfoMap = {
+  [name: string]: NormalizedFileInfo;
+};
 export interface NormalizedFileInfo extends FileInfo {
   __path: string;
   // Compared to `FileInfo` these four props are required here.
@@ -115,7 +118,12 @@
 export class FilesModel extends Model<FilesState> {
   public readonly files$ = select(this.state$, state => state.files);
 
-  public readonly filesWithUnmodified$ = select(
+  /**
+   * `files$` only includes the files that were modified. Here we also include
+   * all unmodified files that have comments with
+   * `status: FileInfoStatus.UNMODIFIED`.
+   */
+  public readonly filesIncludingUnmodified$ = select(
     combineLatest([this.files$, this.commentsModel.commentedPaths$]),
     ([files, commentedPaths]) => addUnmodified(files, commentedPaths)
   );
diff --git a/polygerrit-ui/app/models/comments/comments-model.ts b/polygerrit-ui/app/models/comments/comments-model.ts
index 51b4591..1fdf342 100644
--- a/polygerrit-ui/app/models/comments/comments-model.ts
+++ b/polygerrit-ui/app/models/comments/comments-model.ts
@@ -29,7 +29,6 @@
 } from '../../utils/comment-util';
 import {deepEqual} from '../../utils/deep-util';
 import {select} from '../../utils/observable-util';
-import {RouterModel} from '../../services/router/router-model';
 import {define} from '../dependency';
 import {combineLatest, forkJoin, from, Observable, of} from 'rxjs';
 import {fire, fireAlert, fireEvent} from '../../utils/event-util';
@@ -54,6 +53,7 @@
   switchMap,
 } from 'rxjs/operators';
 import {isDefined} from '../../types/types';
+import {ChangeViewModel} from '../views/change';
 
 export interface CommentState {
   /** undefined means 'still loading' */
@@ -415,7 +415,7 @@
   private discardedDrafts: DraftInfo[] = [];
 
   constructor(
-    private readonly routerModel: RouterModel,
+    private readonly changeViewModel: ChangeViewModel,
     private readonly changeModel: ChangeModel,
     private readonly accountsModel: AccountsModel,
     private readonly restApiService: RestApiService,
@@ -432,7 +432,7 @@
       this.changeModel.patchNum$.subscribe(x => (this.patchNum = x))
     );
     this.subscriptions.push(
-      this.routerModel.routerChangeNum$.subscribe(changeNum => {
+      this.changeViewModel.changeNum$.subscribe(changeNum => {
         this.changeNum = changeNum;
         this.setState({...initialState});
         this.reloadAllComments();
diff --git a/polygerrit-ui/app/models/comments/comments-model_test.ts b/polygerrit-ui/app/models/comments/comments-model_test.ts
index cab36d2..a689e42 100644
--- a/polygerrit-ui/app/models/comments/comments-model_test.ts
+++ b/polygerrit-ui/app/models/comments/comments-model_test.ts
@@ -6,6 +6,7 @@
 import '../../test/common-test-setup';
 import {
   createAccountWithEmail,
+  createChangeViewState,
   createDraft,
 } from '../../test/test-data-generators';
 import {
@@ -20,17 +21,16 @@
 import {
   createComment,
   createParsedChange,
-  TEST_NUMERIC_CHANGE_ID,
 } from '../../test/test-data-generators';
 import {stubRestApi, waitUntil, waitUntilCalled} from '../../test/test-utils';
 import {getAppContext} from '../../services/app-context';
-import {GerritView, routerModelToken} from '../../services/router/router-model';
 import {PathToCommentsInfoMap} from '../../types/common';
 import {changeModelToken} from '../change/change-model';
 import {assert} from '@open-wc/testing';
 import {testResolver} from '../../test/common-test-setup';
 import {accountsModelToken} from '../accounts-model/accounts-model';
 import {ChangeComments} from '../../elements/diff/gr-comment-api/gr-comment-api';
+import {changeViewModelToken} from '../views/change';
 
 suite('comments model tests', () => {
   test('updateStateDeleteDraft', () => {
@@ -72,7 +72,7 @@
 
   test('loads comments', async () => {
     const model = new CommentsModel(
-      testResolver(routerModelToken),
+      testResolver(changeViewModelToken),
       testResolver(changeModelToken),
       testResolver(accountsModelToken),
       getAppContext().restApiService,
@@ -100,10 +100,7 @@
       model.portedComments$.subscribe(c => (portedComments = c ?? {}))
     );
 
-    testResolver(routerModelToken).setState({
-      view: GerritView.CHANGE,
-      changeNum: TEST_NUMERIC_CHANGE_ID,
-    });
+    testResolver(changeViewModelToken).setState(createChangeViewState());
     testResolver(changeModelToken).updateStateChange(createParsedChange());
 
     await waitUntilCalled(diffCommentsSpy, 'diffCommentsSpy');
@@ -133,7 +130,7 @@
     };
     stubRestApi('getAccountDetails').returns(Promise.resolve(account));
     const model = new CommentsModel(
-      testResolver(routerModelToken),
+      testResolver(changeViewModelToken),
       testResolver(changeModelToken),
       testResolver(accountsModelToken),
       getAppContext().restApiService,
@@ -161,7 +158,7 @@
     };
     stubRestApi('getAccountDetails').returns(Promise.resolve(account));
     const model = new CommentsModel(
-      testResolver(routerModelToken),
+      testResolver(changeViewModelToken),
       testResolver(changeModelToken),
       testResolver(accountsModelToken),
       getAppContext().restApiService,
@@ -199,7 +196,7 @@
       })
     );
     const model = new CommentsModel(
-      testResolver(routerModelToken),
+      testResolver(changeViewModelToken),
       testResolver(changeModelToken),
       testResolver(accountsModelToken),
       getAppContext().restApiService,
diff --git a/polygerrit-ui/app/models/views/change.ts b/polygerrit-ui/app/models/views/change.ts
index 31d511a..a206037 100644
--- a/polygerrit-ui/app/models/views/change.ts
+++ b/polygerrit-ui/app/models/views/change.ts
@@ -10,6 +10,7 @@
   BasePatchSetNum,
   ChangeInfo,
   PatchSetNumber,
+  EDIT,
 } from '../../api/rest-api';
 import {Tab} from '../../constants/constants';
 import {GerritView} from '../../services/router/router-model';
@@ -26,18 +27,31 @@
 import {Model} from '../model';
 import {ViewState} from './base';
 
+export enum ChangeChildView {
+  OVERVIEW = 'OVERVIEW',
+  DIFF = 'DIFF',
+  EDIT = 'EDIT',
+}
+
 export interface ChangeViewState extends ViewState {
   view: GerritView.CHANGE;
+  childView: ChangeChildView;
 
   changeNum: NumericChangeId;
   repo: RepoName;
-  edit?: boolean;
   patchNum?: RevisionPatchSetNum;
   basePatchNum?: BasePatchSetNum;
+  /** Refers to comment on COMMENTS tab in OVERVIEW. */
   commentId?: UrlEncodedCommentId;
+
+  // TODO: Move properties that only apply to OVERVIEW into a submessage.
+
+  edit?: boolean;
   /** This can be a string only for plugin provided tabs. */
   tab?: Tab | string;
 
+  // TODO: Move properties that only apply to CHECKS tab into a submessage.
+
   /** Checks related view state */
 
   /** selected patchset for check runs (undefined=latest) */
@@ -61,6 +75,19 @@
   forceReload?: boolean;
   /** triggers opening the reply dialog */
   openReplyDialog?: boolean;
+
+  /** These properties apply to the DIFF child view only. */
+  diffView?: {
+    path?: string;
+    lineNum?: number;
+    leftSide?: boolean;
+  };
+
+  /** These properties apply to the EDIT child view only. */
+  editView?: {
+    path?: string;
+    lineNum?: number;
+  };
 }
 
 /**
@@ -70,7 +97,7 @@
  */
 export type CreateChangeUrlObject = Omit<
   ChangeViewState,
-  'view' | 'changeNum' | 'repo'
+  'view' | 'childView' | 'changeNum' | 'repo'
 > & {
   change: Pick<ChangeInfo, '_number' | 'project'>;
 };
@@ -82,7 +109,9 @@
 }
 
 export function objToState(
-  obj: CreateChangeUrlObject | Omit<ChangeViewState, 'view'>
+  obj:
+    | (CreateChangeUrlObject & {childView: ChangeChildView})
+    | Omit<ChangeViewState, 'view'>
 ): ChangeViewState {
   if (isCreateChangeUrlObject(obj)) {
     return {
@@ -95,15 +124,26 @@
   return {...obj, view: GerritView.CHANGE};
 }
 
-export function createChangeUrl(
-  obj: CreateChangeUrlObject | Omit<ChangeViewState, 'view'>
-) {
-  const state: ChangeViewState = objToState(obj);
-  let range = getPatchRangeExpression(state);
-  if (range.length) {
-    range = '/' + range;
+export function createChangeViewUrl(state: ChangeViewState): string {
+  switch (state.childView) {
+    case ChangeChildView.OVERVIEW:
+      return createChangeUrl(state);
+    case ChangeChildView.DIFF:
+      return createDiffUrl(state);
+    case ChangeChildView.EDIT:
+      return createEditUrl(state);
   }
-  let suffix = `${range}`;
+}
+
+export function createChangeUrl(
+  obj: CreateChangeUrlObject | Omit<ChangeViewState, 'view' | 'childView'>
+) {
+  const state: ChangeViewState = objToState({
+    ...obj,
+    childView: ChangeChildView.OVERVIEW,
+  });
+
+  let suffix = '';
   const queries = [];
   if (state.checksPatchset && state.checksPatchset > 0) {
     queries.push(`checksPatchset=${state.checksPatchset}`);
@@ -136,7 +176,7 @@
     suffix += ',edit';
   }
   if (state.commentId) {
-    suffix = suffix + `/comments/${state.commentId}`;
+    suffix += `/comments/${state.commentId}`;
   }
   if (queries.length > 0) {
     suffix += '?' + queries.join('&');
@@ -144,18 +184,99 @@
   if (state.messageHash) {
     suffix += state.messageHash;
   }
-  if (state.repo) {
-    const encodedProject = encodeURL(state.repo, true);
-    return `${getBaseUrl()}/c/${encodedProject}/+/${state.changeNum}${suffix}`;
-  } else {
-    return `${getBaseUrl()}/c/${state.changeNum}${suffix}`;
+
+  return `${createChangeUrlCommon(state)}${suffix}`;
+}
+
+export function createDiffUrl(
+  obj: CreateChangeUrlObject | Omit<ChangeViewState, 'view' | 'childView'>
+) {
+  const state: ChangeViewState = objToState({
+    ...obj,
+    childView: ChangeChildView.DIFF,
+  });
+
+  const path = `/${encodeURL(state.diffView?.path ?? '', true)}`;
+
+  let suffix = '';
+  // TODO: Move creating of comment URLs to a separate function. We are
+  // "abusing" the `commentId` property, which should only be used for pointing
+  // to comment in the COMMENTS tab of the OVERVIEW page.
+  if (state.commentId) {
+    suffix += `comment/${state.commentId}/`;
   }
+
+  if (state.diffView?.lineNum) {
+    suffix += '#';
+    if (state.diffView?.leftSide) {
+      suffix += 'b';
+    }
+    suffix += state.diffView.lineNum;
+  }
+
+  return `${createChangeUrlCommon(state)}${path}${suffix}`;
+}
+
+export function createEditUrl(
+  obj: Omit<ChangeViewState, 'view' | 'childView'>
+): string {
+  const state: ChangeViewState = objToState({
+    ...obj,
+    childView: ChangeChildView.DIFF,
+    patchNum: obj.patchNum ?? EDIT,
+  });
+
+  const path = `/${encodeURL(state.editView?.path ?? '', true)}`;
+  const line = state.editView?.lineNum;
+  const suffix = line ? `#${line}` : '';
+
+  return `${createChangeUrlCommon(state)}${path},edit${suffix}`;
+}
+
+/**
+ * The shared part of creating a change URL between OVERVIEW, DIFF and EDIT
+ * child views.
+ */
+function createChangeUrlCommon(state: ChangeViewState) {
+  let range = getPatchRangeExpression(state);
+  if (range.length) range = '/' + range;
+
+  let repo = '';
+  if (state.repo) repo = `${encodeURL(state.repo, true)}/+/`;
+
+  return `${getBaseUrl()}/c/${repo}${state.changeNum}${range}`;
 }
 
 export const changeViewModelToken =
   define<ChangeViewModel>('change-view-model');
 
 export class ChangeViewModel extends Model<ChangeViewState | undefined> {
+  public readonly changeNum$ = select(this.state$, state => state?.changeNum);
+
+  public readonly patchNum$ = select(this.state$, state => state?.patchNum);
+
+  public readonly basePatchNum$ = select(
+    this.state$,
+    state => state?.basePatchNum
+  );
+
+  public readonly diffPath$ = select(
+    this.state$,
+    state => state?.diffView?.path
+  );
+
+  public readonly diffLine$ = select(
+    this.state$,
+    state => state?.diffView?.lineNum
+  );
+
+  public readonly diffLeftSide$ = select(
+    this.state$,
+    state => state?.diffView?.leftSide ?? false
+  );
+
+  public readonly childView$ = select(this.state$, state => state?.childView);
+
   public readonly tab$ = select(this.state$, state => state?.tab);
 
   public readonly checksPatchset$ = select(
diff --git a/polygerrit-ui/app/models/views/change_test.ts b/polygerrit-ui/app/models/views/change_test.ts
index b34a1ba..837e362 100644
--- a/polygerrit-ui/app/models/views/change_test.ts
+++ b/polygerrit-ui/app/models/views/change_test.ts
@@ -6,73 +6,145 @@
 import {assert} from '@open-wc/testing';
 import {
   BasePatchSetNum,
-  NumericChangeId,
   RepoName,
   RevisionPatchSetNum,
 } from '../../api/rest-api';
-import {GerritView} from '../../services/router/router-model';
 import '../../test/common-test-setup';
-import {createChangeUrl, ChangeViewState} from './change';
-
-const STATE: ChangeViewState = {
-  view: GerritView.CHANGE,
-  changeNum: 1234 as NumericChangeId,
-  repo: 'test' as RepoName,
-};
+import {
+  createChangeViewState,
+  createDiffViewState,
+  createEditViewState,
+} from '../../test/test-data-generators';
+import {
+  createChangeUrl,
+  createDiffUrl,
+  createEditUrl,
+  ChangeViewState,
+} from './change';
 
 suite('change view state tests', () => {
   test('createChangeUrl()', () => {
-    const state: ChangeViewState = {...STATE};
+    const state: ChangeViewState = createChangeViewState();
 
-    assert.equal(createChangeUrl(state), '/c/test/+/1234');
+    assert.equal(createChangeUrl(state), '/c/test-project/+/42');
 
     state.patchNum = 10 as RevisionPatchSetNum;
-    assert.equal(createChangeUrl(state), '/c/test/+/1234/10');
+    assert.equal(createChangeUrl(state), '/c/test-project/+/42/10');
 
     state.basePatchNum = 5 as BasePatchSetNum;
-    assert.equal(createChangeUrl(state), '/c/test/+/1234/5..10');
+    assert.equal(createChangeUrl(state), '/c/test-project/+/42/5..10');
 
     state.messageHash = '#123';
-    assert.equal(createChangeUrl(state), '/c/test/+/1234/5..10#123');
+    assert.equal(createChangeUrl(state), '/c/test-project/+/42/5..10#123');
   });
 
   test('createChangeUrl() baseUrl', () => {
     window.CANONICAL_PATH = '/base';
-    const state: ChangeViewState = {...STATE};
+    const state: ChangeViewState = createChangeViewState();
     assert.equal(createChangeUrl(state).substring(0, 5), '/base');
     window.CANONICAL_PATH = undefined;
   });
 
   test('createChangeUrl() checksRunsSelected', () => {
     const state: ChangeViewState = {
-      ...STATE,
+      ...createChangeViewState(),
       checksRunsSelected: new Set(['asdf']),
     };
 
     assert.equal(
       createChangeUrl(state),
-      '/c/test/+/1234?checksRunsSelected=asdf'
+      '/c/test-project/+/42?checksRunsSelected=asdf'
     );
   });
 
   test('createChangeUrl() checksResultsFilter', () => {
     const state: ChangeViewState = {
-      ...STATE,
+      ...createChangeViewState(),
       checksResultsFilter: 'asdf.*qwer',
     };
 
     assert.equal(
       createChangeUrl(state),
-      '/c/test/+/1234?checksResultsFilter=asdf.*qwer'
+      '/c/test-project/+/42?checksResultsFilter=asdf.*qwer'
     );
   });
 
   test('createChangeUrl() with repo name encoding', () => {
     const state: ChangeViewState = {
-      view: GerritView.CHANGE,
-      changeNum: 1234 as NumericChangeId,
+      ...createChangeViewState(),
       repo: 'x+/y+/z+/w' as RepoName,
     };
-    assert.equal(createChangeUrl(state), '/c/x%252B/y%252B/z%252B/w/+/1234');
+    assert.equal(createChangeUrl(state), '/c/x%252B/y%252B/z%252B/w/+/42');
+  });
+
+  test('createDiffUrl', () => {
+    const params: ChangeViewState = {
+      ...createDiffViewState(),
+      patchNum: 12 as RevisionPatchSetNum,
+      diffView: {path: 'x+y/path.cpp'},
+    };
+    assert.equal(
+      createDiffUrl(params),
+      '/c/test-project/+/42/12/x%252By/path.cpp'
+    );
+
+    window.CANONICAL_PATH = '/base';
+    assert.equal(createDiffUrl(params).substring(0, 5), '/base');
+    window.CANONICAL_PATH = undefined;
+
+    params.repo = 'test' as RepoName;
+    assert.equal(createDiffUrl(params), '/c/test/+/42/12/x%252By/path.cpp');
+
+    params.basePatchNum = 6 as BasePatchSetNum;
+    assert.equal(createDiffUrl(params), '/c/test/+/42/6..12/x%252By/path.cpp');
+
+    params.diffView = {
+      path: 'foo bar/my+file.txt%',
+    };
+    params.patchNum = 2 as RevisionPatchSetNum;
+    delete params.basePatchNum;
+    assert.equal(
+      createDiffUrl(params),
+      '/c/test/+/42/2/foo+bar/my%252Bfile.txt%2525'
+    );
+
+    params.diffView = {
+      path: 'file.cpp',
+      lineNum: 123,
+    };
+    assert.equal(createDiffUrl(params), '/c/test/+/42/2/file.cpp#123');
+
+    params.diffView = {
+      path: 'file.cpp',
+      lineNum: 123,
+      leftSide: true,
+    };
+    assert.equal(createDiffUrl(params), '/c/test/+/42/2/file.cpp#b123');
+  });
+
+  test('diff with repo name encoding', () => {
+    const params: ChangeViewState = {
+      ...createDiffViewState(),
+      patchNum: 12 as RevisionPatchSetNum,
+      repo: 'x+/y' as RepoName,
+      diffView: {path: 'x+y/path.cpp'},
+    };
+    assert.equal(createDiffUrl(params), '/c/x%252B/y/+/42/12/x%252By/path.cpp');
+  });
+
+  test('createEditUrl', () => {
+    const params: ChangeViewState = {
+      ...createEditViewState(),
+      patchNum: 12 as RevisionPatchSetNum,
+      editView: {path: 'x+y/path.cpp' as RepoName, lineNum: 31},
+    };
+    assert.equal(
+      createEditUrl(params),
+      '/c/test-project/+/42/12/x%252By/path.cpp,edit#31'
+    );
+
+    window.CANONICAL_PATH = '/base';
+    assert.equal(createEditUrl(params).substring(0, 5), '/base');
+    window.CANONICAL_PATH = undefined;
   });
 });
diff --git a/polygerrit-ui/app/models/views/diff.ts b/polygerrit-ui/app/models/views/diff.ts
deleted file mode 100644
index 34f4ee7..0000000
--- a/polygerrit-ui/app/models/views/diff.ts
+++ /dev/null
@@ -1,104 +0,0 @@
-/**
- * @license
- * Copyright 2022 Google LLC
- * SPDX-License-Identifier: Apache-2.0
- */
-import {
-  NumericChangeId,
-  RepoName,
-  RevisionPatchSetNum,
-  BasePatchSetNum,
-  ChangeInfo,
-} from '../../api/rest-api';
-import {GerritView} from '../../services/router/router-model';
-import {UrlEncodedCommentId} from '../../types/common';
-import {
-  encodeURL,
-  getBaseUrl,
-  getPatchRangeExpression,
-} from '../../utils/url-util';
-import {define} from '../dependency';
-import {Model} from '../model';
-import {ViewState} from './base';
-
-export interface DiffViewState extends ViewState {
-  view: GerritView.DIFF;
-  changeNum: NumericChangeId;
-  repo?: RepoName;
-  commentId?: UrlEncodedCommentId;
-  path?: string;
-  patchNum?: RevisionPatchSetNum;
-  basePatchNum?: BasePatchSetNum;
-  lineNum?: number;
-  leftSide?: boolean;
-  commentLink?: boolean;
-}
-
-/**
- * This is a convenience type such that you can pass a `ChangeInfo` object
- * as the `change` property instead of having to set both the `changeNum` and
- * `project` properties explicitly.
- */
-export type CreateChangeUrlObject = Omit<
-  DiffViewState,
-  'view' | 'changeNum' | 'project'
-> & {
-  change: Pick<ChangeInfo, '_number' | 'project'>;
-};
-
-export function isCreateChangeUrlObject(
-  state: CreateChangeUrlObject | Omit<DiffViewState, 'view'>
-): state is CreateChangeUrlObject {
-  return !!(state as CreateChangeUrlObject).change;
-}
-
-export function objToState(
-  obj: CreateChangeUrlObject | Omit<DiffViewState, 'view'>
-): DiffViewState {
-  if (isCreateChangeUrlObject(obj)) {
-    return {
-      ...obj,
-      view: GerritView.DIFF,
-      changeNum: obj.change._number,
-      repo: obj.change.project,
-    };
-  }
-  return {...obj, view: GerritView.DIFF};
-}
-
-export function createDiffUrl(
-  obj: CreateChangeUrlObject | Omit<DiffViewState, 'view'>
-) {
-  const state: DiffViewState = objToState(obj);
-  let range = getPatchRangeExpression(state);
-  if (range.length) range = '/' + range;
-
-  let suffix = `${range}/${encodeURL(state.path || '', true)}`;
-
-  if (state.lineNum) {
-    suffix += '#';
-    if (state.leftSide) {
-      suffix += 'b';
-    }
-    suffix += state.lineNum;
-  }
-
-  if (state.commentId) {
-    suffix = `/comment/${state.commentId}` + suffix;
-  }
-
-  if (state.repo) {
-    const encodedProject = encodeURL(state.repo, true);
-    return `${getBaseUrl()}/c/${encodedProject}/+/${state.changeNum}${suffix}`;
-  } else {
-    return `${getBaseUrl()}/c/${state.changeNum}${suffix}`;
-  }
-}
-
-export const diffViewModelToken = define<DiffViewModel>('diff-view-model');
-
-export class DiffViewModel extends Model<DiffViewState | undefined> {
-  constructor() {
-    super(undefined);
-  }
-}
diff --git a/polygerrit-ui/app/models/views/diff_test.ts b/polygerrit-ui/app/models/views/diff_test.ts
deleted file mode 100644
index 7fab2a4..0000000
--- a/polygerrit-ui/app/models/views/diff_test.ts
+++ /dev/null
@@ -1,64 +0,0 @@
-/**
- * @license
- * Copyright 2022 Google LLC
- * SPDX-License-Identifier: Apache-2.0
- */
-import {assert} from '@open-wc/testing';
-import {
-  BasePatchSetNum,
-  NumericChangeId,
-  RepoName,
-  RevisionPatchSetNum,
-} from '../../api/rest-api';
-import {GerritView} from '../../services/router/router-model';
-import '../../test/common-test-setup';
-import {createDiffUrl, DiffViewState} from './diff';
-
-suite('diff view state tests', () => {
-  test('createDiffUrl', () => {
-    const params: DiffViewState = {
-      view: GerritView.DIFF,
-      changeNum: 42 as NumericChangeId,
-      path: 'x+y/path.cpp' as RepoName,
-      patchNum: 12 as RevisionPatchSetNum,
-      repo: '' as RepoName,
-    };
-    assert.equal(createDiffUrl(params), '/c/42/12/x%252By/path.cpp');
-
-    window.CANONICAL_PATH = '/base';
-    assert.equal(createDiffUrl(params).substring(0, 5), '/base');
-    window.CANONICAL_PATH = undefined;
-
-    params.repo = 'test' as RepoName;
-    assert.equal(createDiffUrl(params), '/c/test/+/42/12/x%252By/path.cpp');
-
-    params.basePatchNum = 6 as BasePatchSetNum;
-    assert.equal(createDiffUrl(params), '/c/test/+/42/6..12/x%252By/path.cpp');
-
-    params.path = 'foo bar/my+file.txt%';
-    params.patchNum = 2 as RevisionPatchSetNum;
-    delete params.basePatchNum;
-    assert.equal(
-      createDiffUrl(params),
-      '/c/test/+/42/2/foo+bar/my%252Bfile.txt%2525'
-    );
-
-    params.path = 'file.cpp';
-    params.lineNum = 123;
-    assert.equal(createDiffUrl(params), '/c/test/+/42/2/file.cpp#123');
-
-    params.leftSide = true;
-    assert.equal(createDiffUrl(params), '/c/test/+/42/2/file.cpp#b123');
-  });
-
-  test('diff with repo name encoding', () => {
-    const params: DiffViewState = {
-      view: GerritView.DIFF,
-      changeNum: 42 as NumericChangeId,
-      path: 'x+y/path.cpp',
-      patchNum: 12 as RevisionPatchSetNum,
-      repo: 'x+/y' as RepoName,
-    };
-    assert.equal(createDiffUrl(params), '/c/x%252B/y/+/42/12/x%252By/path.cpp');
-  });
-});
diff --git a/polygerrit-ui/app/models/views/edit.ts b/polygerrit-ui/app/models/views/edit.ts
deleted file mode 100644
index 3893576..0000000
--- a/polygerrit-ui/app/models/views/edit.ts
+++ /dev/null
@@ -1,60 +0,0 @@
-/**
- * @license
- * Copyright 2022 Google LLC
- * SPDX-License-Identifier: Apache-2.0
- */
-import {
-  EDIT,
-  NumericChangeId,
-  RepoName,
-  RevisionPatchSetNum,
-} from '../../api/rest-api';
-import {GerritView} from '../../services/router/router-model';
-import {
-  encodeURL,
-  getBaseUrl,
-  getPatchRangeExpression,
-} from '../../utils/url-util';
-import {define} from '../dependency';
-import {Model} from '../model';
-import {ViewState} from './base';
-
-export interface EditViewState extends ViewState {
-  view: GerritView.EDIT;
-  changeNum: NumericChangeId;
-  repo: RepoName;
-  path: string;
-  patchNum: RevisionPatchSetNum;
-  lineNum?: number;
-}
-
-export function createEditUrl(state: Omit<EditViewState, 'view'>): string {
-  if (state.patchNum === undefined) {
-    state = {...state, patchNum: EDIT};
-  }
-  let range = getPatchRangeExpression(state);
-  if (range.length) range = '/' + range;
-
-  let suffix = `${range}/${encodeURL(state.path || '', true)}`;
-  suffix += ',edit';
-
-  if (state.lineNum) {
-    suffix += '#';
-    suffix += state.lineNum;
-  }
-
-  if (state.repo) {
-    const encodedProject = encodeURL(state.repo, true);
-    return `${getBaseUrl()}/c/${encodedProject}/+/${state.changeNum}${suffix}`;
-  } else {
-    return `${getBaseUrl()}/c/${state.changeNum}${suffix}`;
-  }
-}
-
-export const editViewModelToken = define<EditViewModel>('edit-view-model');
-
-export class EditViewModel extends Model<EditViewState | undefined> {
-  constructor() {
-    super(undefined);
-  }
-}
diff --git a/polygerrit-ui/app/models/views/edit_test.ts b/polygerrit-ui/app/models/views/edit_test.ts
deleted file mode 100644
index 00bc805..0000000
--- a/polygerrit-ui/app/models/views/edit_test.ts
+++ /dev/null
@@ -1,35 +0,0 @@
-/**
- * @license
- * Copyright 2022 Google LLC
- * SPDX-License-Identifier: Apache-2.0
- */
-import {assert} from '@open-wc/testing';
-import {
-  NumericChangeId,
-  RepoName,
-  RevisionPatchSetNum,
-} from '../../api/rest-api';
-import {GerritView} from '../../services/router/router-model';
-import '../../test/common-test-setup';
-import {createEditUrl, EditViewState} from './edit';
-
-suite('edit view state tests', () => {
-  test('createEditUrl', () => {
-    const params: EditViewState = {
-      view: GerritView.EDIT,
-      changeNum: 42 as NumericChangeId,
-      repo: 'test-project' as RepoName,
-      path: 'x+y/path.cpp' as RepoName,
-      patchNum: 12 as RevisionPatchSetNum,
-      lineNum: 31,
-    };
-    assert.equal(
-      createEditUrl(params),
-      '/c/test-project/+/42/12/x%252By/path.cpp,edit#31'
-    );
-
-    window.CANONICAL_PATH = '/base';
-    assert.equal(createEditUrl(params).substring(0, 5), '/base');
-    window.CANONICAL_PATH = undefined;
-  });
-});
diff --git a/polygerrit-ui/app/services/app-context-init.ts b/polygerrit-ui/app/services/app-context-init.ts
index 1857bad..14fb253 100644
--- a/polygerrit-ui/app/services/app-context-init.ts
+++ b/polygerrit-ui/app/services/app-context-init.ts
@@ -50,12 +50,10 @@
   agreementViewModelToken,
 } from '../models/views/agreement';
 import {ChangeViewModel, changeViewModelToken} from '../models/views/change';
-import {DiffViewModel, diffViewModelToken} from '../models/views/diff';
 import {
   DocumentationViewModel,
   documentationViewModelToken,
 } from '../models/views/documentation';
-import {EditViewModel, editViewModelToken} from '../models/views/edit';
 import {GroupViewModel, groupViewModelToken} from '../models/views/group';
 import {PluginViewModel, pluginViewModelToken} from '../models/views/plugin';
 import {RepoViewModel, repoViewModelToken} from '../models/views/repo';
@@ -112,9 +110,7 @@
     [agreementViewModelToken, () => new AgreementViewModel()],
     [changeViewModelToken, () => new ChangeViewModel()],
     [dashboardViewModelToken, () => new DashboardViewModel()],
-    [diffViewModelToken, () => new DiffViewModel()],
     [documentationViewModelToken, () => new DocumentationViewModel()],
-    [editViewModelToken, () => new EditViewModel()],
     [groupViewModelToken, () => new GroupViewModel()],
     [pluginViewModelToken, () => new PluginViewModel()],
     [repoViewModelToken, () => new RepoViewModel()],
@@ -139,9 +135,7 @@
           resolver(agreementViewModelToken),
           resolver(changeViewModelToken),
           resolver(dashboardViewModelToken),
-          resolver(diffViewModelToken),
           resolver(documentationViewModelToken),
-          resolver(editViewModelToken),
           resolver(groupViewModelToken),
           resolver(pluginViewModelToken),
           resolver(repoViewModelToken),
@@ -154,7 +148,8 @@
       changeModelToken,
       () =>
         new ChangeModel(
-          resolver(routerModelToken),
+          resolver(navigationToken),
+          resolver(changeViewModelToken),
           appContext.restApiService,
           resolver(userModelToken)
         ),
@@ -163,7 +158,7 @@
       commentsModelToken,
       () =>
         new CommentsModel(
-          resolver(routerModelToken),
+          resolver(changeViewModelToken),
           resolver(changeModelToken),
           resolver(accountsModelToken),
           appContext.restApiService,
diff --git a/polygerrit-ui/app/services/flags/flags.ts b/polygerrit-ui/app/services/flags/flags.ts
index 572e107..2a5dff2 100644
--- a/polygerrit-ui/app/services/flags/flags.ts
+++ b/polygerrit-ui/app/services/flags/flags.ts
@@ -22,4 +22,5 @@
   SUGGEST_EDIT = 'UiFeature__suggest_edit',
   MENTION_USERS = 'UiFeature__mention_users',
   RENDER_MARKDOWN = 'UiFeature__render_markdown',
+  REBASE_CHAIN = 'UiFeature__rebase_chain',
 }
diff --git a/polygerrit-ui/app/services/router/router-model.ts b/polygerrit-ui/app/services/router/router-model.ts
index edde7a4..c3c1cb6 100644
--- a/polygerrit-ui/app/services/router/router-model.ts
+++ b/polygerrit-ui/app/services/router/router-model.ts
@@ -4,11 +4,6 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 import {Observable} from 'rxjs';
-import {
-  NumericChangeId,
-  RevisionPatchSetNum,
-  BasePatchSetNum,
-} from '../../types/common';
 import {Model} from '../../models/model';
 import {select} from '../../utils/observable-util';
 import {define} from '../../models/dependency';
@@ -18,9 +13,7 @@
   AGREEMENTS = 'agreements',
   CHANGE = 'change',
   DASHBOARD = 'dashboard',
-  DIFF = 'diff',
   DOCUMENTATION_SEARCH = 'documentation-search',
-  EDIT = 'edit',
   GROUP = 'group',
   PLUGIN_SCREEN = 'plugin-screen',
   REPO = 'repo',
@@ -31,9 +24,6 @@
 export interface RouterState {
   // Note that this router model view must be updated before view model state.
   view?: GerritView;
-  changeNum?: NumericChangeId;
-  patchNum?: RevisionPatchSetNum;
-  basePatchNum?: BasePatchSetNum;
 }
 
 export const routerModelToken = define<RouterModel>('router-model');
@@ -43,17 +33,6 @@
     state => state.view
   );
 
-  readonly routerChangeNum$: Observable<NumericChangeId | undefined> = select(
-    this.state$,
-    state => state.changeNum
-  );
-
-  readonly routerPatchNum$: Observable<RevisionPatchSetNum | undefined> =
-    select(this.state$, state => state.patchNum);
-
-  readonly routerBasePatchNum$: Observable<BasePatchSetNum | undefined> =
-    select(this.state$, state => state.basePatchNum);
-
   constructor() {
     super({});
   }
diff --git a/polygerrit-ui/app/test/test-data-generators.ts b/polygerrit-ui/app/test/test-data-generators.ts
index 23a5794..f0a4cbe 100644
--- a/polygerrit-ui/app/test/test-data-generators.ts
+++ b/polygerrit-ui/app/test/test-data-generators.ts
@@ -105,7 +105,6 @@
 import {EditRevisionInfo, ParsedChangeInfo} from '../types/types';
 import {
   DetailedLabelInfo,
-  FileInfo,
   QuickLabelInfo,
   SubmitRequirementExpressionInfo,
   SubmitRequirementResultInfo,
@@ -115,8 +114,8 @@
 import {Category, RunStatus} from '../api/checks';
 import {DiffInfo} from '../api/diff';
 import {SearchViewState} from '../models/views/search';
-import {ChangeViewState} from '../models/views/change';
-import {EditViewState} from '../models/views/edit';
+import {ChangeChildView, ChangeViewState} from '../models/views/change';
+import {NormalizedFileInfo} from '../models/change/files-model';
 
 const TEST_DEFAULT_EXPRESSION = 'label:Verified=MAX -label:Verified=MIN';
 export const TEST_PROJECT_NAME: RepoName = 'test-project' as RepoName;
@@ -400,10 +399,15 @@
   return messages;
 }
 
-export function createFileInfo(): FileInfo {
+export function createFileInfo(
+  path = 'test-path/test-file.txt'
+): NormalizedFileInfo {
   return {
     size: 314,
     size_delta: 7,
+    lines_deleted: 0,
+    lines_inserted: 0,
+    __path: path,
   };
 }
 
@@ -701,6 +705,7 @@
 export function createChangeViewState(): ChangeViewState {
   return {
     view: GerritView.CHANGE,
+    childView: ChangeChildView.OVERVIEW,
     changeNum: TEST_NUMERIC_CHANGE_ID,
     repo: TEST_PROJECT_NAME,
   };
@@ -716,12 +721,22 @@
   };
 }
 
-export function createEditViewState(): EditViewState {
+export function createEditViewState(): ChangeViewState {
   return {
-    view: GerritView.EDIT,
+    view: GerritView.CHANGE,
+    childView: ChangeChildView.EDIT,
     changeNum: TEST_NUMERIC_CHANGE_ID,
     patchNum: EDIT,
-    path: 'foo/bar.baz',
+    repo: TEST_PROJECT_NAME,
+    editView: {path: 'foo/bar.baz'},
+  };
+}
+
+export function createDiffViewState(): ChangeViewState {
+  return {
+    view: GerritView.CHANGE,
+    childView: ChangeChildView.DIFF,
+    changeNum: TEST_NUMERIC_CHANGE_ID,
     repo: TEST_PROJECT_NAME,
   };
 }
diff --git a/polygerrit-ui/app/types/types.ts b/polygerrit-ui/app/types/types.ts
index 8d55e36..557e3a0 100644
--- a/polygerrit-ui/app/types/types.ts
+++ b/polygerrit-ui/app/types/types.ts
@@ -10,7 +10,6 @@
   AccountInfo,
   BasePatchSetNum,
   ChangeViewChangeInfo,
-  CommitId,
   CommitInfo,
   EditPatchSet,
   PatchSetNum,
@@ -28,11 +27,6 @@
   requestAvailability(): void;
 }
 
-export interface CommitRange {
-  baseCommit: CommitId;
-  commit: CommitId;
-}
-
 export type {CoverageRange} from '../api/diff';
 export {CoverageType} from '../api/diff';
 
diff --git a/polygerrit-ui/app/utils/comment-util.ts b/polygerrit-ui/app/utils/comment-util.ts
index 8af5beb..a92f0f8 100644
--- a/polygerrit-ui/app/utils/comment-util.ts
+++ b/polygerrit-ui/app/utils/comment-util.ts
@@ -598,3 +598,17 @@
       .includes(account.email)
   );
 }
+
+export function findComment(
+  comments: {
+    [path: string]: (CommentInfo | DraftInfo)[];
+  },
+  commentId: UrlEncodedCommentId
+) {
+  if (!commentId) return undefined;
+  let comment;
+  for (const path of Object.keys(comments)) {
+    comment = comment || comments[path].find(c => c.id === commentId);
+  }
+  return comment;
+}
diff --git a/polygerrit-ui/app/utils/path-list-util.ts b/polygerrit-ui/app/utils/path-list-util.ts
index 1116123..b007d47 100644
--- a/polygerrit-ui/app/utils/path-list-util.ts
+++ b/polygerrit-ui/app/utils/path-list-util.ts
@@ -4,7 +4,7 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 import {SpecialFilePath, FileInfoStatus} from '../constants/constants';
-import {FileInfo} from '../types/common';
+import {FileInfo, FileNameToFileInfoMap} from '../types/common';
 import {hasOwnProperty} from './common-util';
 
 export function specialFilePathCompare(a: string, b: string) {
@@ -55,7 +55,7 @@
 // In case there are files with comments on them but they are unchanged, then
 // we explicitly displays the file to render the comments with Unchanged status
 export function addUnmodifiedFiles(
-  files: {[filename: string]: FileInfo},
+  files: FileNameToFileInfoMap,
   commentedPaths: {[fileName: string]: boolean}
 ) {
   if (!commentedPaths) return;
diff --git a/polygerrit-ui/app/utils/path-list-util_test.ts b/polygerrit-ui/app/utils/path-list-util_test.ts
index 50f5c0e..3c9e0d3 100644
--- a/polygerrit-ui/app/utils/path-list-util_test.ts
+++ b/polygerrit-ui/app/utils/path-list-util_test.ts
@@ -12,9 +12,9 @@
   specialFilePathCompare,
   truncatePath,
 } from './path-list-util';
-import {FileInfo} from '../api/rest-api';
 import {hasOwnProperty} from './common-util';
 import {assert} from '@open-wc/testing';
+import {FileNameToFileInfoMap} from '../types/common';
 
 suite('path-list-utl tests', () => {
   test('special sort', () => {
@@ -117,7 +117,7 @@
       'file1.txt': true,
     };
 
-    const files: {[filename: string]: FileInfo} = {
+    const files: FileNameToFileInfoMap = {
       'file2.txt': {
         status: FileInfoStatus.REWRITTEN,
         size_delta: 10,
diff --git a/resources/com/google/gerrit/server/mime/mime-types.properties b/resources/com/google/gerrit/server/mime/mime-types.properties
index 2f9561b..8e97ba7 100644
--- a/resources/com/google/gerrit/server/mime/mime-types.properties
+++ b/resources/com/google/gerrit/server/mime/mime-types.properties
@@ -39,6 +39,7 @@
 cpp = text/x-c++src
 cql = text/x-cassandra
 cxx = text/x-c++src
+cu = text/x-c++src
 cyp = application/x-cypher-query
 cypher = application/x-cypher-query
 c++ = text/x-c++src